IIOLOGY  UBRARY 

)rnla  Institute  of  Technology 


14  -  DAYS 


STUDIES  OF 


INHERITANCE  IN  GUINEA-PIGS  AND  RATS 


BY 


W.  E.  CASTLE  AND  SEWALL  WRIGHT 


PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  or  WASHINGTON 
WASHINGTON,  1916 


CARNEGIE  INSTITUTION  OF  WASHINGTON,  PUBLICATION  No.  241 


PAPER  No.  26  OF  THE  STATION  FOR  EXPERIMENTAL  EVOLUTION 
AT  COLD  SPRING  HARBOR,  NEW  YORK 

FROM  THE  LABORATORY  OF  GENETICS 
OF  THE  BUSSEY  INSTITUTION 


Copies  of  this  Book 

were  first  issued 

SEP  20  1916 


PRESS  OF  GIBSON  BROTHERS,  INC. 
WASHINGTON 


CONTENTS. 

PART  I. — AN  EXPEDITION  TO  THE  HOME  OF  THE  GUINEA-PIG  AND   SOME   BREEDING 
EXPERIMENTS  WITH  MATERIAL  THERE  OBTAINED.    BY  W.  E.  CASTLE. 

PAGE. 

Introduction 3 

Some  observations  on  guinea-pigs  in  Peru 5 

Hybridization  experiments  with  Cavia  cutleri 8 

Life  history  of  C.  cutleri 8 

Crosses  of  C.  cutleri  males  with  guinea-pig  females 13 

Color  inheritance  among  the  F2  hybrids 13 

(a)  Cross  9  albino  (race  B)  X  d"  C.  cutleri 13 

(6)  Cross  9  albino  (race  C)  X  d"  C.  cutleri 14 

(c)  Cross  9  brown-eyed  cream  (race  C)  X  d"  C.  cutleri 16 

(d)  Results  from  (6)  and  (c)  combined 16 

(e)  Intensity  and  dilution  among  the  hybrids 17 

(/)   Significance  of  the  results  observed 18 

Hybridization  experiments  with  a  race  of  feral  guinea-pigs  from  lea,  Peru 20 

Origin  and  characteristics  of  the  lea  race 20 

Crosses  between  the  lea  race  and  guinea-pigs  of  race  C 23 

The  F2  generation 24 

Summary  on  the  lea  race 29 

Hybridization  experiments  with  a  domesticated  guinea-pig  from  Arequipa 31 

d1  1002  and  his  FI  offspring 31 

F,  offspring  of  d"  1002 33 

Back-cross  and  other  offspring  of  d"1  1002 35 

Miscellaneous  matings  of  the  descendants  of  d"  1002 36 

Summary  on  the  Arequipa  domesticated  race 41 

Size  inheritance  in  guinea-pig  crosses 42 

Previous  work  on  size  inheritance 42 

Weights  and  growth  curves  of  C.  cutleri,  of  various  guinea-pig  races,  and  of  their 

hybrids 43 

Skeletal  measurements  of  C.  cutleri,  of  various  races  of  guinea-pigs,  and  of  their 

hybrids 47 

The  C.  cutleri  hybrids 48 

Hybrids  of  the  Arequipa  d"  1002 52 

The  lea  hybrids 53 

Theoretical  explanations  of  size  inheritance  and  of  "blending  inheritance" 

in  general 54 

PART  II. — AN  INTENSIVE  STUDY  OF  THE  INHERITANCE  OF  COLOR  AND  OF  OTHER  COAT 
CHARACTERS  IN  GUINEA-PIGS,  WITH  ESPECIAL  REFERENCE  TO  GRADED  VARIATIONS. 
BY  SEW  ALL  WRIGHT. 

PAGE. 

Color  and  its  inheritance  in  guinea-pigs 59 

Skin,  fur,  and  eye  colors  of  guinea-pigs 59 

Color  of  Cavia  cutleri 59 

Melanin  pigment 59 

Primary  classification  of  fur  colors 59 

Yellow  group  of  colors 60 

Dark  group  of  colors 60 

Skin  colors 61 

Eye  colors 62 

Definitions  of  fur  colors  by  Ridgway's  charts 62 

Definitions  of  eye  colors 63 

Heredity  of  fur  and  eye  color 63 

Color  factors  of  guinea-pigs 63 

Classification  of  color  factors . .  63 


IV  CONTENTS. 

Color  and  its  inheritance  in  guinea-pigs — Continued.  PAGE. 

Heredity  of  fur  and  eye  color— Continued. 

Color  vs.  white 64 

Intensity  of  general  color  development 64 

Dark  vs.  yellow  color 65 

Variations  of  dark  color 66 

Table  of  factor  combinations 66 

Hereditary  factors  and  the  physiology  of  pigment 67 

Discussion  of  experiments 74 

Material 74 

Systematic  position 74 

Description  of  stocks 74 

Problems 77 

Inheritance  of  dilution 77 

The  red-eye  factor 77 

Dilution 79 

The  dilution  factor 80 

Inheritance  of  minor  variations  in  intensity 85 

Methods  and  accuracy  of  grading 85 

Variations  in  intense  guinea-pigs  and  albinos 85 

Multiple  allelomorphs 86 

The  relations  of  imperfect  dominance,  stock,  and  age  to  grades  of  intensity . .  87 

Variations  of  yellow 89 

Variations  of  sepia 92 

Variations  of  eye  color 93 

Summary " 93 

Inheritance  of  variations  in  the  agouti  pattern 94 

Previous  work 95 

The  inheritance  of  the  agouti  of  C.  rufescens 96 

Minor  variations 99 

The  inheritance  of  the  agouti  of  C.  cutleri 100 

Inheritance  of  rough  fur 100 

Classification 102 

Previous  work 102 

Material 103 

Problems 104 

Inheritance  of  rough  as  opposed  to  smooth 105 

Inheritance  of  major  variations 106 

Possibilities  of  linkage  among  rough  and  color  factors 113 

Summary  of  rough  tables 115 

Minor  variations 116 

Roughness  of  series  II 117 

Summary 118 

General  conclusion 119 

Experimental  data 121 

Explanation  of  tables  62  to  137 121 

PART  III.  FURTHER  STUDIES  OF  PIEBALD  RATS  AND  SELECTION,  WITH  OBSERVATIONS 
ON  GAMETIC  COUPLING.    BY  W.  E.  CASTLE. 

PAGE. 

The  progeny  of  hooded  rats  twice  crossed  with  wild  rats 163-168 

A  second  report  on  mass  selection  of  the  hooded  pattern  of  rats 168-172 

Further  observations  on  the  mutant  series 173-174 

Gametic  coupling  in  yellow  rats 175-180 

Tables 181-187 

BIBLIOGRAPHY 188-190 

EXPLANATION  OP  PLATES.  . .  ...  191-192 


PART  I 

AN  EXPEDITION  TO  THE  HOME  OF  THE  GUINEA-PIG 

AND  SOME  BREEDING  EXPERIMENTS  WITH 

MATERIAL  THERE  OBTAINED 


BY  W.  E.  CASTLE 


INTRODUCTION. 

For  several  years  I  have  been  engaged  in  studies  of  heredity  in 
guinea-pigs.  In  the  course  of  these  studies  all  the  common  varieties 
of  guinea-pigs  have  been  investigated  by  the  method  of  experimental 
breeding  and  something  has  been  learned  concerning  their  inter- 
relationships and  probable  mode  of  origin.  The  actual  origin  of  most 
of  these  varieties  is,  however,  unknown,  as  is  true  also  concerning 
most  varieties  of  domesticated  animals.  One  or  two  varieties  have, 
however,  been  made  synthetically  in  the  laboratory  and  it  is  conceivable 
that,  if  we  had  the  original  wild  stock  to  work  with,  from  which  the 
domesticated  guinea-pig  has  arisen,  some  or  all  of  the  existing  varieties 
might  be  synthesized  anew  and  perhaps  still  others  might  be  obtained, 
and  that  in  this  way  something  might  be  learned  of  the  method  by 
which  new  varieties  arise.  From  considerations  such  as  these  I  have 
for  several  years  been  seeking  to  obtain  living  specimens  of  the  wild 
species  which  most  closely  resemble  guinea-pigs.  In  1903  I  received 
from  Campinas,  Brazil,  3  wild-caught  individuals  referred  at  the  tune 
to  the  species  Cavia  aperea,  but  since  found  to  agree  better  with  the 
description  of  C.  rufescens.  From  two  of  these  animals  young  were 
obtained,  and  crosses,  the  results  of  which  have  been  described  in 
detail  by  Dr.  Detlefsen  (1914),  were  made  with  domesticated  guinea- 
pigs.  It  may  be  noted  that  all  male  FI  hybrids  were  sterile,  but  that 
the  FI  females  were  fertile,  and  that  upon  repeated  crossing  of  these 
with  male  guinea-pigs,  a  race  of  fertile  hybrids  was  at  last  obtained, 
these  being,  in  the  language  of  breeders,  about  £  guinea-pig,  |  rufescens. 
From  this  result  it  seems  doubtful  whether  C.  rufescens  has  any  close 
genetic  relationship  to  the  domesticated  guinea-pig,  although  by 
hybridization  it  has  been  found  possible  to  produce  races  (f  or  more 
guinea-pig)  which  have  derived  certain  characters  from  a  rufescens 
ancestor. 

Cavia  aperea  from  Argentina  has  been  crossed  with  the  guinea-pig 
by  Nehring  (1893,  1894)  in  Berlin,  with  the  production  of  fully  fertile 
hybrids.  This  result  indicates  a  closer  relationship  with  the  guinea-pig 
than  C.  rufescens  manifests.  Darwin  (1876),  however,  did  not  regard 
aperea  as  the  ancestor  of  the  guinea-pig,  because  he  found  it  to  be 
infested  with  a  different  species  of  louse.  I  have  not  myself  been  able 
as  yet  to  obtain  specimens  of  C.  aperea.  Nehring  (1889)  has  argued 
with  much  plausibility  that  Cavia  cutleri  of  Peru  is  more  probably  the 
ancestor  of  the  guinea-pig,  for  (1)  it  agrees  closely  with  the  guinea-pig 
in  cranial  characters  and  it  occurs  in  a  region  where  guinea-pigs  have 
been  for  a  long  time  kept  in  domestication,  as  is  shown  by  the  occurrence 
of  mummified  guinea-pigs  which  had  been  buried  with  the  dead.  Natu- 
rally I  formed  a  strong  desire  to  secure  living  specimens  of  C.  cutleri  for 

3 


4  INTRODUCTION. 

experimental  study,  but  for  several  years  I  was  unable  to  do  so. 
Through  correspondence  with  Professor  S.  I.  Bailey,  who  was  at  the 
tune  director  of  the  Harvard  Astronomical  Observatory  at  Arequipa, 
Peru,  I  ascertained  that  a  wild  species  of  cavy  occurred  in  that  locality. 
Professor  Bailey  kindly  captured  some  of  the  cavies  and  attempted 
repeatedly  to  forward  them  to  me,  but  without  success.  The  steam- 
ship companies  refused  to  accept  them  for  transportation  on  the  ground 
that  they  might  lead  to  detention  or  quarantining  of  their  vessels, 
since  all  rodents  were  suspected  of  being  carriers  of  bubonic  plague. 
After  several  years  of  waiting  and  fruitless  negotiation  with  every 
chance  traveler  to  Peru  with  whom  I  came  in  contact,  I  resolved  to 
go  to  Peru  myself  and  get  the  desired  specimens.  Through  a  grant 
made  by  the  Carnegie  Institution  of  Washington  I  was  enabled,  in  the 
fall  of  1911,  to  carry  this  resolution  into  effect. 

The  Carnegie  Institution  of  Washington  and  the  Bussey  Institution 
have  together  provided  means  for  carrying  out  the  breeding  experi- 
ments described  in  this  paper.  I  wish  to  express  my  gratitude  to  both 
institutions  and  to  thank  the  director  and  other  officers  of  the  Harvard 
College  Observatory  for  hospitality  and  generous  assistance  given  me 
at  the  Arequipa  station.  I  am  indebted  also  to  Professor  C.  J.  Brues 
for  kindly  bringing  me  a  stock  of  guinea-pigs  obtained  by  him  near 
Lima,  Peru,  in  1912. 


SOME  OBSERVATIONS  ON  GUINEA-PIGS  IN  PERU. 

On  a  midsummer  day  in  December  1911  I  arrived  as  a  guest  at  the 
Harvard  College  Observatory  in  Arequipa,  Peru,  where  I  went  in 
search  of  guinea-pigs,  wild  and  domesticated,  to  be  used  in  breeding 
experiments. 

The  day  after  my  arrival  at  the  observatory  I  walked  a  short  dis- 
tance up  the  highway  through  a  group  of  adobe  cabins,  straw-thatched 
and  without  chimney  or  windows,  and  with  a  single  door.  On  looking 
in  at  the  open  door  of  one  of  the  cabins,  I  was  pleased  to  see  a  domesti- 
cated guinea-pig  of  the  common  spotted  black-and-white  sort  familiar 
to  lovers  of  pet-stock  throughout  the  world.  In  other  near-by  cabins 
I  found  considerable  numbers  of  guinea-pigs  were  kept,  in  one  as  many 
as  40.  They  were  fed  on  fresh-cut  alfalfa  or  the  green  leaves  of  maize, 
receiving  apparently  no  other  food  and  no  water.  At  the  back  or 
sides  of  the  cabin  was  a  sort  of  shelf  or  bench  of  stone  used  as  a  seat 
or  couch,  underneath  which  the  guinea-pigs  had  their  home.  Their 
escape  through  the  open  door  was  prevented  by  a  high  lintel  of  stone, 
perhaps  15  inches  (38  cm.)  high,  over  which  one  has  to  step  in  entering. 
In  these  cabins  were  seen  most  of  the  common  color  varieties  of  guinea- 
pigs  known  to  us,  agouti,  black,  yellow,  and  white  (albino).  None  of 
the  colored  individuals  which  I  saw  was  self-colored;  all  were  spotted 
with  white  or  with  yellow  or  in  both  ways.  The  same  predilection  for 
spotting  is  seen  in  the  other  important  native  domesticated  animal,  the 
llama.  I  saw  no  llamas  except  such  as  were  spotted;  some  were  black 
spotted  with  white,  but  the  majority  were  of  a  soft  shade  of  buff  or 
fawn  spotted  with  white.  The  common  spotted  condition  of  our 
guinea-pigs  is  undoubtedly  one  of  long  standing;  indeed  it  would  seem 
that  the  Peruvian  natives  breed  no  other  variety  except  such  as  are 
either  white  spotted  or  all  white.  The  unspotted  or  "  self-colored " 
varieties  now  kept  by  fanciers  in  Europe  and  America  have  probably 
been  produced  by  selection  from  stock  originally  spotted.  This  is 
indicated  by  the  great  difficulty  in  securing  a  self-colored  race  entirely 
free  from  spotted  individuals.  Most  self-colored  races,  even  when  bred 
for  many  generations  from  self-colored  ancestors  exclusively,  will  pro- 
duce an  occasional  individual  bearing  a  few  hairs  or  a  patch  of  hairs  of 
some  other  color,  or  of  white. 

Among  the  guinea-pigs  kept  by  the  natives  near  Arequipa,  I  observed 
an  occasional  animal  having  a  rough  or  resetted  coat.  This  variety  is 
known  to  fanciers  in  Europe  and  the  United  States  under  the  name 
Abyssinian.  (See  Castle,  1905.)  It  is  said,  on  the  authority  of 
Geoffrey  Saint-Hilaire,  to  have  been  introduced  from  Peru  into  Europe 
about  the  year  1872  in  a  rough-coated,  long-haired  individual  received 
at  the  Jardin  d'Acclimatation,  Paris.  In  conformity  with  this  account 

5 


6  INHERITANCE    IN   GUINEA-PIGS. 

it  may  be  said  that  the  rough-coated  long-haired  variety  has  ever  since 
its  introduction  been  called  by  fanciers  "  Peruvian."  I  saw  no  long- 
haired individuals,  either  rough-coated  or  smooth,  among  the  guinea- 
pigs  kept  by  the  natives  at  Arequipa,  and  the  short-haired  rough-coated 
ones  observed  had  imperfectly  developed  rosettes,  much  inferior  to 
the  best  standard-bred  resetted  Abyssinians  of  fanciers  in  Europe  and 
the  United  States.  For  this  reason  I  infer  that  no  particular  attention 
was  given  to  this  character  in  the  breeding  of  the  guinea-pigs  which  I 
saw,  though  this  may  very  likely  have  been  done  in  other  parts  of  the 
country.  But  the  unit-character  variation  which  is  responsible  for  the 
resetted  condition  of  the  coat  in  Abyssinian  guinea-pigs  was  plainly 
represented  in  the  stocks  kept  by  the  natives  in  Arequipa  and  needed 
only  selection  to  bring  it  up  to  the  standards  of  fanciers. 

Eight  independent  mendelizing  unit-character  variations  had  been 
recognized  as  affecting  the  coat  characters  of  guinea-pigs  up  to  this 
time.  Six  of  these  were  represented  among  the  four  or  five  dozen 
guinea-pigs  which  I  actually  saw  in  the  cabins  of  natives,  the  other 
two  unit  characters  being  (1)  the  long-haired  variation  which,  as 
already  noted,  is  said  to  have  been  brought  originally  from  Peru  to 
Europe;  and  (2)  the  brown  variation  which  first  came  to  the  notice 
of  fanciers  in  England  about  1900  and  was  certainly  in  existence  before 
that  time  in  the  United  States,  as  I  can  state  from  personal  knowledge. 
It  is  uncertain  whether  or  not  this  last  variation  had  already  occurred 
in  Peru  and  was  thence  transferred  to  Europe,  but  it  is  certain  that  all 
the  other  7  had  done  so,  and  it  is  very  probable  that  this  also  originated 
in  Peru.  Further,  a  ninth  wholly  independent  unit-character  variation 
(presently  to  be  described,  viz,  the  pink-eyed  variation)  has  made  its 
appearance  in  stocks  of  domesticated  guinea-pigs  obtained  by  me  at 
Arequipa  in  1911  and  by  my  colleague,  Professor  C.  T.  Brues,  at  Luna, 
in  1912.  So  it  is  clear  that  this  variation  also  is  widely  disseminated 
among  domesticated  guinea-pigs  kept  by  the  natives  in  Peru  and  which 
have  never  been  in  the  hands  of  European  fanciers  at  all. 

It  can  be  stated,  therefore,  with  probable  correctness,  that  the  guinea- 
pig  has  undergone  in  domestication  more  extensive  variation  in  color 
and  coat  characters  than  any  other  mammal,  and  that  this  variation 
has  occurred  almost  if  not  quite  exclusively  under  the  tutelage  of  the 
natives  of  Peru.  This  conclusion  points  either  to  a  great  antiquity 
of  the  guinea-pig  as  a  domesticated  animal  or  to  more  rapid  evolution  by 
unit  character  variation  than  by  other  natural  processes. 

That  the  natives  do  give  careful  attention  to  the  selection  of  animals 
for  breeding  is  shown  by  the  following  incident :  In  the  cabin  near  the 
observatory,  where  I  first  saw  guinea-pigs  in  Peru,  and  where  I  ulti- 
mately secured  two  pairs  of  animals,  one  of  which  I  brought  back  with 
me,  I  observed  a  very  large  individual  which  I  desired  to  purchase, 
and  though  other  individuals  were  offered  me  at  a  very  reasonable  price, 


GUINEA-PIGS   IN   PERU.  7 

this  particular  one  could  not  be  had  because,  I  was  assured,  he  was  the 
"padre"  (sire)  of  the  entire  family.  Size  seemed  to  be  the  point 
especially  emphasized  in  the  breeding  of  guinea-pigs  hi  this  cabin,  as 
would  naturally  be  the  case  when  the  animals  formed  the  meat-supply 
of  the  family,  as  they  do  now  among  the  native  poor  of  Peru  and  doubt- 
less have  done  since  ancient  times. 

But  the  chief  object  of  my  journey  to  Peru  was  the  study  not  of  the 
domesticated  guinea-pigs  of  the  country,  but  of  their  wild  progenitors. 
Accordingly  special  efforts  were  made  to  secure  specimens  of  the  wild 
cavy,  which  Professor  Bailey  had  found  to  be  abundant  hi  the  locality. 
Once  or  twice,  when  riding  along  a  road  between  irrigated  fields,  I  had 
seen  a  cavy  scurry  to  cover  in  a  pile  of  rocks;  further,  I  had  observed 
droppings  of  the  animals  in  the  rocky  wall  of  a  cattle  corral  in  an 
alfalfa  field.  But  how  to  capture  the  animals  alive  was  a  problem 
which  baffled  immediate  solution.  It  seemed  likely  that  the  natives 
would  know  better  how  to  go  about  this  than  I  did.  Accordingly  word 
was  passed  around  among  the  near-by  villages  that  a  good  price  would 
be  paid  at  the  observatory  for  wi!4  cavies,  either  alive  or  dead. 
Within  a  few  hours  boys  began  to  arrive  with  the  coveted  specimens 
and  for  the  next  week  I  was  kept  busy  preparing  skins  and  saving  bones 
of  the  animals  which  were  received  dead,  or  making  cages  and  caring 
for  such  as  arrived  alive.  In  this  way  11  cavies  (all  I  could  hope  to 
transport  safely)  and  about  a  dozen  skins  were  soon  secured,  and 
preparations  were  made  for  the  return  journey.  In  due  time  the 
journey  was  accomplished,  and  with  such  success  that  three  new  races 
of  guinea-pigs  were  added  to  our  experimental  stocks,  viz,  (1)  a  wild 
species,  the  probable  ancestor  of  the  domesticated  guinea-pig,  identified 
as  Cavia  cutleri  Bennett;  (2)  a  feral  race  from  lea,  probably  identical 
with  that  described  by  Von  Tschudi;  (3)  domesticated  guinea-pigs, 
such  as  are  at  present  kept  by  the  natives  of  Peru. 


8  INHERITANCE    IN   GUINEA-PIGS. 


HYBRIDIZATION  EXPERIMENTS  WITH  CAVIA  CUTLERI. 
LIFE  HISTORY  OF  CAVIA  CUTLERI. 

The  primary  object  of  my  journey  to  Peru  was  to  secure  representa- 
tives of  the  wild  species  of  cavy,  Cavia  cutleri  Bennett,  known  to  exist 
there.  Four  pairs  of  these  animals  captured  at  Arequipa  were  suc- 
cessfully installed  in  cages  at  the  Bussey  Institution  in  January  1913. 

One  of  the  males  soon  died  without  leaving  descendants;  the  other 
7  animals  (4  females  and  3  males)  produced  offspring  in  captivity,  which 
have  continued  to  breed  succesfully,  though  the  stock  has  at  times 
been  seriously  reduced  by  disease  in  cold  weather.  Three  generations 
of  descendants  have  been  reared  from  the  original  stock  of  7  animals. 
Together  they  number  100  individuals,  of  which  47  are  males  and  53 
females.  All  are  very  uniform  in  color,  size,  general  appearance,  and 
behavior. 

Their  color  is  a  dull  leaden  gray-brown,  well  adapted  to  escape  notice 
amid  the  arid  surroundings  of  their  native  habitat.  The  fur  is  agouti- 
ticked  and  the  belly  light,  but  the  yellow  of  the  ticking  and  belly  is  so 
pale  as  to  resemble  a  dirty  white  or  very  light  cream  shade.  The  color 
is  much  paler  than  that  of  the  Brazilian  species,  Cavia  rufescens,  studied 
by  Detlefsen.  The  fur  is  also  finer  and  softer,  in  which  respect  it 
resembles  the  guinea-pig.  The  size  of  C.  cutleri  is  about  the  same  as 
that  of  C.  rufescens,  and  between  one-third  and  one-half  that  of  the 
guinea-pig.  The  maximum  weight  of  an  adult  male  is  about  525  grams ; 
that  of  a  domesticated  male  guinea-pig  obtained  in  Arequipa  (of  1002) 
is  nearly  three  times  this  amount. 

In  wildness  Cavia  cutleri  is  very  much  like  C.  rufescens.  The  animals 
live  contentedly  in  small  cages,  2  feet  6  inches  square,  but  invariably 
retreat  under  their  box  or  conceal  themselves  in  the  hay  if  anyone 
approaches. 

The  extreme  savageness  toward  each  other  of  individuals  of  Cavia 
cutleri  makes  it  difficult  to  rear  large  numbers  of  them  in  captivity.  It 
is  seldom  possible  to  keep  more  than  a  single  pair  in  a  cage  together 
for  any  length  of  tune.  Two  adult  males  will  not  five  together  peace- 
ably under  any  circumstances,  and  if  two  females  are  placed  together 
in  a  cage  with  one  male  persecution  of  one  female  by  the  other  usually 
follows.  Even  when  the  young  are  allowed  to  grow  up  in  the  same 
cage  with  their  parents,  family  dissensions  are  likely  to  arise  as  soon  as 
the  young  become  mature. 

The  period  of  gestation  (minimum  interval  between  litters)  averages  3 
or  4  days  shorter  than  in  guinea-pigs,  being  60  to  70  days,  and  the  number 
of  young  to  a  litter  varies  from  1  to  4.  Fifty-three  litters  born  in  captivity 
include  exactly  100  young,  an  average  of  1.89  young  to  a  litter.  The 
size  of  litter  occurring  most  frequently  is  2,  which  has  been  recorded 


CAVIA   CUTLERI. 


9 


TABLE  1. — Number  and  size  of  litters  produced  by  each  mother,  Cavia  cutleri. 


Mother  and  date  of  her  birth. 

Date  of  litter. 

Size  of 
litter. 

Mother's 
age  at 
birth  of 
young. 

Days 
since 
last 
litter. 

9  2  (caught  wild)  ;  born  March  1911  (?)  

Mar.  5,  1913 

2 

months 
24 

9  3  (caught  wild)  ;  born  May  1911  (?)  

June  28,  1913 
Aug.  29,  1913 
Nov.  4,  1913 

May  29,  1912 

2 
2 
2 

3 

27 
29 
31 

12 

62 
67 

9  5  (caught  wild)  ;  born  Jan.  1910  (?)  

Oct.  3,  1912 
Dec.  26,  1912 
July  5,  1913 
Dec.  15,  1913 

July  12,  1912 

3 
1 
3 
1 

3 

17 
20 
26 
32 

18 

9  6  (caught  wild)  ;  born  Jan.  1910  (?)  

Sept.  12,  1912 
Nov.  15,  1912 
Jan.  22,  1913 

Sept.  6,  1912 

3 
3 
2 

3 

20 
22 

24 

20 

62 
64 
68 

9  11;  May  29,  1912  

Sept.  26,  1912 

1 

4 

9  15;  July  12,  1912  

Dec.  10,  1912 

2 

5 

926;  Sept.  6,  1912  ,.  

Feb.  17,  1913 
June  30,  1913 
Oct.  1,  1913 
Aug.  15,  1914 
Dec.  2,  1914 

July  5,  1912 

1 
3 
2 
2 
1 

1 

7 
12 
15 
25 
29 

10 

69 

927;  Sept.  6,  1912  

Sept.  4,  1912 
Nov.  4,  1912 

Apr.  25,  1913 

2 
2 

1 

12 
14 

7 

61 
61 

9  36;  Oct.  3,  1912  

June  25,  1913 
Aug.  25,  1913 

June  17,  1913 

1 
1 

1 

9 
11 

8 

61 
61 

942;  Nov.  15,  1912  

Oct.  16,  1913 
Aug.  3,  1914 
Nov.  2,  1914 

July  26,  1913 

4 
2 
2 

2 

12 
22 
25 

8 

965;  Jan.  22,  1913  

Sept.  20,  1913 
Aug.  25,  1914 
Nov.  2,  1914 

July  26,  1913 

2 
2 
2 

2 

10 
21 
24 

6 

56 
69 

966;  Jan.  22,  1913  

Nov.  1,  1913 
Dec.  27,  1913 

June  25,  1913 

2 
3 

2 

9 
11 

5 

56 

9  79;  March  5,  1913  

Aug.  29,  1913 
June  28,  1913 

2 
1 

7 
3|t 

65 

9  118;  June  28,  1913  

Sept.  4,  1913 
Nov.  4,  1913 

2 
1 

6 
4 

68 

9  124;  June  30,  1913  

Jan.  5,  1914 
Nov.  1  1913 

1 
3 

6 
4 

62 

9129;  July  5,  1913  

Dec.  27,  1913 

2 

6 

9  184;  Sept.  4,  1913  

Mar.  1,  1914 
Mar.  15,  1914 

1 
1 

8 
6 

64 

9224;  Oct.  16,  1913  

May  18,  1914 
July  20,  1914 

July  30,  1913 

1 
2 

1 

8 
10 

9 

64 
63 

9  241  ;  Nov.  4,  1913  

Dec.  8,  1913 
Jan.  12,  1915 

1 
2 

14 
14 

10 


INHERITANCE   IN   GUINEA-PIGS. 


24  times;  litters  of  1  have  been  recorded  18  times,  litters  of  3, 10  times, 
and  a  litter  of  4  once.  Factors  which  influence  size  of  litter  are  evi- 
dently age  and  state  of  nourishment  of  the  mother.  Table  2  shows  the 
relation  of  age  of  mother  to  size  of  litter.  Very  young  mothers  (age 
4  months  or  less)  have  only  1  young  at  a  birth.  The  females  become 
sexually  mature  at  a  very  early  age,  as  do  female  guinea-pigs.  Well- 
nourished  females  may  breed  at  2  months  of  age,  when  they  are  less 
than  half-grown,  full  growth  not  being  attained  until  they  are  12  or  13 
months  old.  Females  over  4  months  but  under  12  months  of  age 
produce  usually  1  or  2  young  at  a  birth,  rarely  3;  those  which  are  1  or 
2  years  old  produce  the  maximum  number  of  young,  usually  2  or  3, 
rarely  1  or  4.  After  the  age  of  2  years  the  number  of  young  again 

TABLE  2. — Relation  between  age  of  mother  and  size  of  litter,  Cavia  cuileri. 


Age  of  mother 
in  months. 

Size  of  litters  and  number  of 
each  size. 

Age  of  mother 
in  months. 

Size  of  litters  and  number  of 
each  size. 

1  in 
litter. 

2  in 

litter. 

3  in 

litter. 

4  in 
litter. 

1  in 
litter. 

2in 
litter. 

3  in 

litter. 

4  in 
litter. 

4  

3 

2 
3 
1 
1 
1 
2 

1 
1 

12  to  15  

1 

3 
1 
2 
6 
2 

2 
2 
3 
1 

1 

5  

16  to  19  

6  

1 
3 
3 
2 
1 
1 

20  to  23  

1 

7  

24  to  27  

8  

28  to  31  

1 
1 

9  

32  

10 

Total  litters.  .  . 

11  

18 

24 

10 

1 

decreases  to  1  or  2.  The  oldest  female  known  to  have  borne  young 
(one  of  the  original  stock)  had  at  the  time  been  in  captivity  over  2 
years  and  her  estimated  age  was  32  months.  None  of  the  females 
born  in  captivity  has  given  birth  to  young  at  a  more  advanced  age 
than  29  months.  Our  records  accordingly  indicate  that  females  rarely 
breed  after  they  have  attained  the  age  of  1\  years.  The  duration  of 
the  breeding  period  in  the  case  of  males  is  more  extended.  It  is  prob- 
able that  males  do  not  attain  sexual  maturity  quite  so  early  as  females, 
for  females  may  breed  when  less  than  2  months  old,  but  we  have  no 
evidence  that  males  can  breed  before  they  are  3  months  old.1  But  the 
capacity  to  breed  once  attained  continues  indefinitely.  One  male 
(cT4)  caught  wild  in  December  1911  and  estimated  then  to  have  been 
6  months  old  is  still  siring  young,  more  than  3  years  after  his  capture, 
being,  it  is  estimated,  nearly  4  years  old. 

Females  are  capable  of  breeding  again  immediately  after  the  birth 
of  a  litter,  but  if  they  do  so  the  number  of  young  at  the  next  birth  is 

*Mr.  Wright  has  called  my  attention  to  a  record  from  his  experiments  which  shows  that  a  male 
guinea-pig  containing  a  slight  infusion  of  rufescens  blood  must  have  been  sexually  mature  at  2J 
months  of  age.  This  is  the  only  record  known  to  me  of  a  guinea-pig  male  breeding  when  less 
than  3  months  old. 


CAVIA   CUTLERI. 


11 


apt  to  be  less,  or  the  young  will  be  born  smaller  and  less  fully  developed 
(with  smaller  bodies  and  shorter  hair),  and  the  period  of  gestation  will 
be  shortened,  even  to  56  days  in  extreme  cases,  the  normal  period  being, 
as  in  the  guinea-pig,  between  60  and  70  days.  (See  table  4.)  If  the 
mother  is  well  nourished  and  has  not  borne  a  litter  recently,  she  is  more 
likely  to  have  a  large  litter  of  young.  The  largest  litter  recorded  (4)  was 
borne  by  a  female  1  year  old,  which  had  previously  had  only  1  young, 
born  4  months  earlier.  The  recorded  date  of  the  birth  of  each  litter  of 
young  is  given  in  table  1,  together  with  the  interval  in  days  between  suc- 
cessive litters  by  the  same  mother,  except  in  cases  where  the  interval  is 
obviously  greater  than  the  ordinary  period  of  gestation,  and  it  is  to 

TABLE  3. — Relation  of  size  of  litter  and  number  of  litters  to  time  of  year. 


Size  of  litters  and  number 
of  each  size. 

Total 
litters. 

Total 
young. 

1  in 
litter. 

2  in 
Utter. 

3  in 

litter. 

4  in 
litter. 

January  

1 

1 
2 
1 
1 
3 

2 
1 

2 

1 

3 
1 
3 
1 
2 
5 

5 
1 

4 
1 

4 

7 

February  

March  

April  

May  

June  

Total  born  in  first 
6  months1  

9 

6 

1 

0 

15 

22 

July  

2 

1 
1 

3 
5 
3 
1 
5 
2 

3 

2 
1 
2 
1 

1 

8 
6 
6 
3 

8 

7 

17 
11 
13 
9 
17 
11 

August  

September  

October  

November  

1 

4 

December  

Total  born  in  sec- 
ond 6  months2.  . 

9 

19 

9 

1 

38 

78 

1  Average,  1 .47  young  per  litter. 


2Average,  2.05  young  per  litter. 


be  supposed  that  the  mother  did  not  breed  again  immediately.  The 
variation  in  these  day  intervals  between  litters  is  shown  in  table  4, 
from  which  it  appears  that  the  gestation  period  ordinarily  continues 
from  61  to  69  days,  with  63.3  days  as  an  average.  However,  the 
periods  as  recorded  can  not  be  relied  upon  as  accurate,  except  within 
limits  of  about  2  days,  for  the  cages  were  not  inspected  daily,  but  only 
once  or  twice  a  week,  and  when  young  more  than  24  hours  old  were 
found  in  a  cage,  the  estimated  age  of  the  young  may  differ  from  the 
true  age  by  1  or  2  days.  Young  less  than  a  day  old  are  readily  recog- 
nized as  such  by  the  condition  of  the  umbilical  cord. 

The  4  original  wild-caught  females  have  a  somewhat  better  record  of 
productiveness  than  their  descendants  reared  in  captivity,  which  indi- 


12 


INHERITANCE   IN   GUINEA-PIGS. 


cates  that  laboratory  conditions  of  close  captivity  are  not  as  favorable 
for  full  growth  and  vigor  as  the  freer  life  and  better  air  of  the  original 
habitat.  The  4  wild-caught  females  produced  33  young  in  14  litters,  an 
average  of  2.36  young  to  a  litter.  Their  daughters  or  granddaughters, 
reared  in  captivity,  when  of  like  age,  have  produced  27  young  in  13 
litters,  an  average  of  2.07  young  to  a  litter. 

Too  much  emphasis  must  not  be  laid,  however,  on  this  difference, 
because  productiveness  depends  largely  on  food,  care,  and  weather  con- 
ditions, and  it  is  not  certain  that  these  were  equally  favorable  for  the 
original  females  and  for  their  descendants,  respectively. 

Table  1  shows  for  each  mother  how  many  litters  of  young  she  has 
borne,  at  what  age  she  bore  them,  and  how  many  young  were  contained 
in  each  litter.  In  the  case  of  the  4  females  caught  wild,  the  age  given 
for  the  mother  is  of  course  not  known;  the  age  recorded  is  an  estimate 
based  on  the  size  of  the  mother  when  captured. 

Table  3  shows  in  what  month  each  litter  of  young  was  born  and  what 
its  size  was.  This  table  brings  out  rather  strikingly  the  effect  of  the 
seasons  and  consequent  character  of  food  available  upon  the  size  and 
number  of  the  litters. 

TABLE  4. — Variation  in  period  of  gestation  (interval  since  previous  litter) 
in  Cavia  cutteri.    Average,  63.8  days. 


Days 

Days 

between 

Cases. 

between 

Cases. 

litters. 

litters. 

56 

2 

65 

1 

61 

4 

67 

1 

62 

3 

68 

2 

63 

1 

69 

2 

64 

3 

In  the  6  months  from  July  to  December  inclusive,  litters  were  born 
which  were  conceived  under  summer  conditions,  with  an  abundance  of 
green  food  available.  It  will  be  observed  that  in  this  half  of  the  year 
the  litters  are  numerous  (38)  and  large  (average  2.05  young  to  a  litter). 
The  young  born  in  the  6  months  January  to  June  inclusive  were  con- 
ceived under  winter  conditions,  when  the  mothers  were  subsisting 
largely  on  a  diet  of  dried  or  concentrated  foods,  with  a  limited  amount 
of  green  food  available.  In  this  half  of  the  year  the  litters  are  less 
numerous  (15)  and  smaller  (average  size  1.47  young). 

Temperature  probably  does  not  directly  affect  the  result,  as  the 
animals  were  kept  in  a  heated  house,  but  purity  of  the  air  may  possibly 
do  so,  as  the  house  is  much  better  ventilated  in  the  warmer  months. 
But  food  is  probably  the  most  important  factor,  as  the  condition  of  the 
animals  changes  promptly  with  change  of  food,  even  when  other  condi- 
tions show  no  change. 


CROSSES   OF   CAVIA   CTJTLERI.  13 

CROSSES  OF  CAVIA  CUTLERI  MALES  WITH  GUINEA-PIG  FEMALES. 

Crosses  have  been  made  only  between  male  Cavia  cutleri  and  female 
guinea-pigs.  The  reciprocal  cross  was  not  undertaken,  because  the 
number  of  cutleri  females  on  hand  at  any  one  time  has  been  insufficient 
and  because  it  seemed  probable  that  a  cross  with  the  much  larger 
guinea-pig  would  be  fatal  to  the  cutleri  females  because  of  the  probable 
large  size  of  the  hybrid  offspring.  Two  races  of  guinea-pigs  were 
employed  in  the  crosses,  these  being  the  purest  races  available,  the 
genetic  properties  of  which  had  been  long  and  thoroughly  tested. 

The  race  most  extensively  used  may  be  called  race  C.  It  consisted 
of  "brown-eyed  cream"  individuals  or  of  albinos  borne  by  brown-eyed 
cream  parents.  The  results  of  crosses  of  colored  and  albino  individuals 
of  race  C  will  be  described  separately.  The  other  race  may  be  called 
race  B.  It  consisted  of  intensely  black-pigmented  individuals  or  of 
albinos  produced  by  such  black  individuals.  The  results  of  crosses  with 
the  two  sorts  of  individuals  will  be  described  separately.  A  cutleri  male 
bred  in  captivity  (cf  78)  was  mated  with  black  females  of  race  B,  and 
produced  9  FI  young,  all  colored  like  C.  cutleri,  but  darker,  the  ticking 
of  the  fur  being  brick  red  or  yellow  instead  of  creamy  white  as  in  cutleri. 

Albino  females  of  race  B  were  mated  with  the  same  cutleri  male 
(c?78)  or  with  cfH4,  another  cutleri  male  reared  in  captivity,  or  else 
with  cT4  or  c?8,  which  were  original  cutleri  males  caught  wild.  Such 
matings  produced  39  FI  young,  all  with  the  same  (golden  agouti)  type 
of  coloration  as  the  young  produced  by  the  black  mothers. 

Females  of  race  C  were  mated  only  with  the  two  wild-caught  cutleri 
males  (cf4  and  cf8).  The  cream-colored  mothers  of  race  C  produced 
34  young,  all  golden  agouti  in  color  like  the  young  derived  from  race  B 
crosses,  but  much  lighter.  They  were,  however,  darker  in  color  than 
C.  cutleri,  the  agouti  ticking  being  yellow  or  reddish,  not  creamy  white 
as  in  cutleri.  (See  plate  3.)  Albino  females  of  race  C  produced  by  the 
cutleri  males  14  young,  indistinguishable  in  appearance  from  the  young 
produced  by  their  cream-colored  sisters. 

The  FI  hybrids,  whose  total  number  was  96,  were  all  vigorous  and 
large,  their  adult  size  nearly  or  quite  equaling  that  of  guinea-pigs. 
They  grew  with  great  rapidity  and  have  proved  fully  fertile  inter  se. 
In  wildness  and  ferocity  they  are  intermediate  between  the  parent  races. 

COLOR  INHERITANCE  AMONG  THE  F2  HYBRIDS. 

(a)  CROSS  9  ALBINO  (RACE  B)  X  rf  CUTLERI. 

By  breeding  inter  se  certain  of  the  F!  hybrids,  from  the  cross  9 
albino,  race  B,  X  cf  cutleri  there  has  been  produced  a  second  (or  F2) 
generation  of  hybrids,  which  number  75  individuals.  As  regards  color, 
disregarding  minor  differences  of  intensity  of  pigmentation,  these 
hybrids  fall  into  three  classes:  golden  agouti,  black,  and  albino.  Of  the 


14 


INHERITANCE   IN   GUINEA-PIGS. 


agoutis  there  are  43,  of  the  blacks  15,  and  of  the  albinos  17.  The 
numerical  relations  of  the  classes  suggest  a  dihybrid  Mendelian  ratio 
of  9:3:4,  which  is  in  entire  agreement  with  existing  knowledge  of 
color  inheritance  in  guinea-pigs  (Castle,  1905;  Sollas,  1909).  C.  cutleri 
is  evidently  homozygous  for  all  Mendelian  color  factors,  since  it  breeds 
very  true  to  color.  Albino  guinea-pigs  from  a  black  race  are  known 
to  possess  two  independent  recessive  modifications  from  this  condition, 
lacking  both  the  agouti  factor  and  the  so-called  color  factor.  As 
regards  these  factors,  then,  the  wild  race,  cutleri,  forms  gametes  AC,  the 
albino  forms  gametes  ac,  and  the  F!  hybrids  form  gametes  of  the  four 
types  AC,  Ac,  aC,  and  ac.  From  recombination  of  such  gametes 
should  arise  in  F2  zygotes  as  in  table  5. 


TABLE  5. 


1  AACC 

2  AaCC 
2  AACc 
4  AaCc 

9  agouti 


1  aaCC 

2  aaCc 


3  black 


1  AAcc 

2  Aacc 


3  albino 


1  albino 


The  several  kinds  of  albinos  being  similar  in  appearance,  the  expected 
result  is  9  agouti,  3  black,  4  albino.  The  agreement  with  this  expecta- 
tion is  fairly  close  (see  table  6). 


TABLE  6. 


Agouti. 

Black. 

Albino. 

Observed  

43 

15 

17 

Expected  

42.19 

14.06 

18.75 

(b)  CROSS  9  ALBINO  (RACE  C)  X  <?  CUTLERI. 

FI  animals  from  the  cross  between  an  albino  of  race  C  and  a  cutleri 
male  have  produced  44  F2  young,  which  fall  into  7  color  classes,  dis- 
regarding differences  of  intensity  of  pigmentation.  These  classes  and 
their  numerical  representation  among  the  44  young  are  as  follows: 
golden  agouti,  10;  black,  1;  cinnamon,  8;  black-eyed  cream,  4;  brown- 
eyed  cream,  3;  chocolate,  4;  albino,  14.  (See  plate  4.)  The  occurrence 
of  these  several  classes  of  F2  young  is  what  previously  existing  knowl- 
edge of  color  inheritance  among  guinea-pigs  would  have  led  us  to  expect, 
for  it  was  known  that  albinos  of  race  C  differed  from  agoutis  in  the  same 
two  factors  as  the  albinos  of  race  B,  viz,  the  agouti  factor  and  the  color 
factor.  In  addition,  the  albinos  of  race  C  were  known  to  differ  from 
agoutis  in  two  other  factors,  seen  respectively  in  chocolate  and  yellow 
races.  The  chocolate  race  may  be  considered  to  have  arisen  by  a 
recessive  modification  of  the  black  factor  B,  and  the  yellow  race  by  a 
similar  modification  of  the  extension  factor  E.  Accordingly  this  cross 


CROSSES  OF  CAVIA  CUTLERI. 


15 


was  supposed  in  advance  to  involve  4  independent  Mendelian  factors,  a 
supposition  which  the  observed  result  justifies.  The  factor  differences 
in  the  two  races  are:  gametes  of  cutleri,  ABCE;  of  albino  (race  C),  abce. 
On  this  hypothesis  the  FI  hybrids  should  form  16  different  kinds  of  gam- 
etes, the  color  potentialities  of  which  are  indicated  in  parentheses: 


1  ABCE  (agouti). 

2  aBCE  (black). 

3  AbCE  (cinnamon). 

4  ABcE   (albino). 

5  ABCe   (black-eyed  yellow). 

6  ABce    (albino). 


7  AbcE  (albino). 

8  abCE  (chocolate). 

9  aBCe  (black-eyed  yellow). 

10  aBcE  (albino). 

11  AbCe  (brown-eyed  yellow). 


12  Abce  (albino). 

13  aBce  (albino). 

14  abCe  (brown-eyed  yellow). 

15  abcE  (albino). 

16  abce  (albino). 


From  this  list  it  will  be  observed  that  2  different  gametic  factorial 
combinations  are  capable  of  producing  black-eyed  yellow,  and  that 
the  same  is  true  concerning  brown-eyed  yellow,  while  8  different  com- 
binations contain  the  potentialities  of  albinos.  From  these  considera- 
tions it  follows  that  the  F2  ratio  will  be  peculiar,  since  each  of  the  yellow 
classes  that  can  be  distinguished  from  each  other  (black-eyed  and 
brown-eyed)  will  itself  be  composite,  and  the  same  will  be  true  of  the 
albino  class.  The  expected  classes  and  their  proportional  frequencies 
will  accordingly  be: 


Golden  agouti 81 

Black 27 

Cinnamon 27 

Yellow  (black-eyed) 36 


Yellow  (brown-eyed) 12 

Chocolate 9 

Albino .  .  .64 


A  cross  involving  the  formation  of  so  many  classes  of  individuals  can 
not  be  expected  to  show  very  satisfactory  Mendelian  ratios  in  so  small 
a  number  of  offspring  as  44.  All  the  expected  classes  are  represented, 
although  black  is  represented  in  a  single  individual  only. 

The  colored  individuals  of  race  C  were  known  in  many  cases  to  carry 
albinism  as  a  recessive  character.  The  albino  gametes  of  such  indi- 
viduals would,  in  crosses  with  cutleri  mates,  form  the  same  kind  of 
zygotes  as  the  albinos  of  race  C,  which  were  used  in  the  cross  just 
described.  In  considering  the  results  of  such  crosses,  it  is  therefore 
proper  to  include  in  one  category  FI  animals  derived  from  both  sources. 
If  this  is  done  the  F2  young  are  increased  to  108,  distributed  as  shown 
in  table  7,  the  expected  theoretical  number  in  each  class  being  shown  in 
a  parallel  column. 

TABLE  7. 


Observed. 

Expected. 

Observed. 

Expected. 

Golden  agouti  

33 

34.17 

Chocolate  ...        ... 

7 

3.80 

Black  

7 

11.39 

Albino   ... 

27 

27.00 

13 

11  39 

Black-eyed  yellow  .... 
Brown-eyed  yellow  

13 

8 

15.08 
5.07 

108 

108.00 

16 


INHERITANCE   IN   GUINEA-PIGS. 


(c)  CROSS  9  BROWN-EYED  CREAM  (RACE  C)  X  d1  CUTLERI. 

The  F!  animals  produced  by  crossing  brown-eyed  cream  females  of 
race  C  with  cutleri  males  themselves  produced  132  F2  young,  distributed 
among  the  same  7  classes  as  the  albino  cross  had  produced  (table  8). 

TABLE  8. 


Observed. 

Expected. 

Observed. 

Expected. 

Golden  agouti  

57 

48.94 

Chocolate  

5 

5.44 

Black  

17 

16.31 

Albino  

16 

10 

16  31 

Black-eyed  yellow  .... 
Brown-eyed  yellow  .... 

19 

8 

21.75 
7.25 

132 

116.00 

Except  in  regard  to  albinos,  the  result  expected  from  this  cross  is  the 
same  as  that  expected  from  crossing  albinos  of  race  C.  Accordingly 
the  albinos  may  be  for  the  moment  disregarded.  The  expectation  as 
regards  the  colored  classes  of  young  may  then  be  stated  as  shown  in  the 
column  of  " observed"  results. 

The  occurrence  of  16  albinos  in  this  F2  generation  shows  that  certain 
of  the  F!  pah's  were  heterozygous  for  this  character,  which  they  obvi- 
ously derived  from  the  brown-eyed  cream  parent,  not  from  the  cutleri 
parent;  for  the  brown-eyed  cream  animals  of  race  C  were  known  in 
many  cases  to  be  capable  of  producing  albinos,  whereas  the  cutleri  stock 
bred  true.  Accordingly  such  pairs  of  FI  animals  from  this  cross  as  pro- 
duced albino  young  should  be  tabulated  with  the  hybrids  produced  by 
crossing  albinos  of  race  C  with  cutleri  males.  If  this  is  done  there 
remain  68  instead  of  116  F2  young  to  be  considered.  Among  these  are 
3  albinos  which  it  is  impossible  to  transfer  to  table  7,  because  it  is  not 
known  what  colored  individuals  were  born  in  the  same  litters  with  them. 
They  were  born  in  a  pen  containing  2  females  which  had  young  simul- 
taneously, one  of  which  was  known  to  produce  albino  young,  though 
the  other  did  not.  Omitting  the  3  albinos,  there  remain  65  colored 
young,  distributed  as  shown  in  table  9. 

TABLE  9. 


Observed. 

Expected. 

Observed. 

Expected. 

Golden  agouti  

34 

27.42 

Brown-eyed  yellow  .... 

3 

4.06 

Black  

11 

9  14 

Chocolate                  .  . 

2 

3.05 

914 

Black-eyed  yellow.  .  .  . 

10 

12.19 

65 

65.00 

(d)  RESULTS  FROM  (b)  AND  (c)  COMBINED. 

Since  the  expectation  is  the  same  as  regards  the  relative  proportions 
of  the  several  colored  classes  hi  all  crosses  of  race  C  feihales  (whether 
albino  or  colored)  with  cutleri  males,  we  may  legitimately  combine  all 


CROSSES  OF  CAVIA  CUTLERI. 


17 


the  F2  results,  omitting  only  albinos  (which  have  been  dealt  with 
already).  When  this  is  done  we  get  the  results  shown  in  table  10. 
No  class  deviates  from  expectation  enough  to  suggest  " linkage"  or 
"coherence"  of  characters  involved  in  the  cross. 


TABLE  10. 


Observed. 

Expected. 

Observed. 

Expected. 

Golden  agouti  .  .      .    . 

67 

61  59 

Brown-eyed  yellow 

11 

9  13 

Black  

18 

20  53 

Chocolate 

9 

6  85 

18 

20  53 

Black-eyed  yellow.  .  .  . 

23 

27.37 

146 

146.00 

(e)  INTENSITY  AND  DILUTION  AMONG  THE  HYBRIDS. 

It  has  been  stated  that  the  FI  young  produced  by  the  cross  of  female 
albinos  of  race  B  with  male  cutleri  were  dark  golden  agouti  in  color, 
much  darker  than  the  cutleri  parent.  This  darkening  of  the  color  per- 
sisted undiminished  into  the  following  generation  (F2).  Of  the  58 
colored  FI  young  derived  from  this  cross  none  was  as  light  in  coloration 
as  the  cutleri  grandparent.  Hence  it  would  appear  that  the  darker 
coloration  introduced  by  the  cross,  apparently  through  the  albino 
parent,  does  not  behave  as  a  simple  Mendelian  character  either  domi- 
nant or  recessive;  otherwise  pale-colored  F2  young  should  have  been 
produced.  Whatever  factors,  Mendelian  or  otherwise,  are  responsible 
for  the  darkening  of  the  pigmentation  are  evidently  unconnected  with 
the  so-called  color  factor,  since  they  are  transmitted  by  albinos,  which 
lack  this  factor. 

A  very  different  result  was  observed  in  crosses  of  the  same  cutleri 
males  with  females  of  race  C.  The  colored  animals  of  race  C  are  very 
pale  cream-colored.  The  Fx  young  which  they  produced  showed  a 
more  intense  yellow  than  either  parent,  but  were  much  lighter  than  the 
hybrids  produced  in  the  cross  with  race  B  albinos.  (See  plate  3.) 

Among  their  F2  young  appeared  some  very  light-colored  individuals, 
16  being  recorded  in  a  total  of  56  young  produced  by  pairs  which  pro- 
duced no  albinos.  The  pale-colored  young  were  not  confined  to  any 
one  colored  class,  but  were  recorded  among  the  agoutis,  blacks,  cinna- 
mons, and  yellows.  (See  table  11.)  The  proportion  recorded  is  close 
to  one-fourth,  from  which  it  would  seem  that  dilution  had  been  intro- 
duced as  a  recessive  character  by  the  cream  guinea-pig  grandparents. 
Since,  however,  C.  cutleri  is  relatively  pale  in  pigmentation,  it  is  prob- 
able that  some  of  the  animals  classified  as  pale  were  not "  dilute,"  owing 
to  a  factor  derived  from  the  guinea-pig  ancestor,  but  because  of  condi- 
tions derived  from  the  cutleri  ancestor.  This  statement  applies  to  the 
young  of  matings  which  produced  albinos  as  well  as  to  those  which  did 
not.  The  significant  thing  is  that  more  pale-pigmented  young  and 
those  which  excelled  in  paleness  were  obtained  from  those  matings 
which  did  not  involve  albinsim. 


18 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  11. — Distribution  of  intensity  and  dilution  among  the  F%  young  derived 
from  the  cross  9  race  CX  <?  cutleri. 


Color  variety  of  young. 

From  pairs  pro- 
ducing no  albinos. 

From  pairs  pro- 
ducing albinos. 

Intense. 

Dilute. 

Intense. 

Dilute. 

Agouti  

25 
5 
2 
5 
2 
1 

8 
3 
3 

2 

28 
6 
13 
10 
6 
7 

4 
1 

4 
2 

Black  

Cinnamon  

Black-eyed  yellow  

Brown-eyed  yellow  

Chocolate  

Total  

40 

16 

70 

11 

It  was  expected  that  albinos  of  race  C  would  produce  a  much  larger 
proportion  of  pale-colored  grandchildren,  but  strange  to  say  this  expec- 
tation was  not  realized;  81  F2  colored  young  produced  in  matings 
which  yielded  albinos  (showing  that  the  guinea-pig  characters  had  been 
received  through  albino  gametes)  included  only  11  pale-colored  young, 
and  none  of  these  is  recorded  as  being  paler  in  color  than  the  cutleri 
grandparent.  It  would  appear,  therefore,  that  the  albino  gametes  of 
race  C  mothers  do  not  transmit  the  dilution  seen  in  the  cream-colored 
animals  of  race  C.  This  would  be  a  puzzling  state  of  affairs  had  not 
Wright  (1915)  already  discovered  an  easy  explanation  for  it,  viz,  that 
the  dilution  of  the  cream  race  is  an  allelomorph  of  albinism,  and  so  can 
not  be  transmitted  in  the  same  gamete  with  albinism. 

Comparing  the  F2  hybrids  derived  from  race  C  crosses  with  those 
derived  from  race  B  crosses,  it  is  certain  that  the  pigmentation  of  both 
is  darker  than  that  of  wild  C.  cutleri,  but  the  intensity  of  the  race  B 
hybrids  much  exceeds  that  of  the  race  C  hybrids.  Among  the  race  B 
hybrids  no  evidence  can  be  discovered  of  segregating  Mendelian  inten- 
sity factors;  among  the  race  C  hybrids  dilution  segregates  as  a  simple 
Mendelian  recessive,  precisely  as  does  albinism,  but  apparently  no 
gamete  transmits  both  dilution  and  albinism,  for  the  reason  that  they 
are  alternative  conditions  of  the  same  factor.  Aside  from  the  factorial 
difference  in  dilution,  how  does  race  B  differ  from  race  C?  Apparently 
in  no  simple  factorial  way,  but  in  a  general  way  as  regards  energy  of 
pigment  production,  in  which  hybrids  of  both  races  surpass  C.  cutleri 
but  differ  quantitatively  from  each  other.  No  Mendelian  explanation 
of  this  difference  is  at  present  justified  by  the  observations  made. 

(f)  SIGNIFICANCE  OF  THE  RESULTS  OBSERVED. 

The  complete  fertility  of  the  hybrids  produced  by  crossing  wild  Cavia 
cutleri  with  the  guinea-pig  is  in  striking  contrast  with  the  sterility  of 
hybrids  between  C.  rufescens  and  the  guinea-pig,  as  observed  by  Det- 


CROSSES   OF   CAVIA   CUTLERI.  19 

lefsen.  This  indicates  that  C.  cutleri  from  Peru  is  the  actual  wild 
ancestor  of  the  guinea-pig  or  closely  related  to  that  ancestor.  Since, 
however,  Nehring  has  reported  that  C.  aperea  (from  Argentina)  also 
produces  fertile  hybrids  with  the  guinea-pig,  it  seems  likely  that  these 
two  species  are  closely  related  to  each  other  and  might  interbreed  freely 
if  their  respective  ranges  were  not  completely  separated.  It  seems 
possible  also  that  both  species  have  contributed  to  the  production  of  the 
domesticated  form,  or  that  still  other  species  have  shared  in  producing 
it.  Further  observations  are  needed  to  clear  up  this  matter. 

It  is  evident  that  the  mendelizing  unit-character  differences,  which 
distinguish  one  variety  of  domesticated  guinea-pig  from  another,  also 
exist  between  guinea-pigs  and  the  wild  Cavia  cutleri.  They  are  inherited 
in  precisely  the  same  way  among  the  hybrids  produced  by  crossing 
guinea-pigs  with  C.  cutleri  as  in  crosses  of  one  variety  of  guinea-pig  with 
another — that  is,  they  mendelize.  It  is  evident  that  these  variations 
have  arisen  by  a  process  of  retrogressive  or  loss  variation.  For  example, 
in  the  matter  of  color  varieties  such  as  black,  brown,  yellow,  and  white, 
which  (in  relation  to  the  parent  form)  are  known  to  breed  true  without 
exception,  it  is  evident  that  these  have  arisen  by  loss  (or  retrogressive 
modification)  of  physiological  processes  which  occur  in  the  wild  species, 
since  crosses  with  the  wild  form  bring  them  back  in  a  heterozygous 
state,  after  which  they  continue  to  form  all  possible  permutations  and 
recombinations  with  each  other.  Thus  albinos  of  race  C  (which  breed 
true  inter  se  and  without  crossing  with  some  other  variety  could  pro- 
duce no  other  sort)  if  crossed  with  C.  cutleri  (which  also  breeds  true) 
produce  in  F2  a  definite  series  of  color  varieties.  This  series  includes 
all  the  color  varieties  of  guinea-pigs  more  commonly  known,  such  as  (1) 
golden  agouti,  (2)  black,  (3)  cinnamon,  (4)  chocolate,  (5)  black-eyed 
yellow,  (6)  brown-eyed  yellow,  and  (7)  albino. 

The  mode  of  origin  of  the  color  varieties  of  guinea-pigs  (and  by 
inference  of  other  domesticated  animals  also)  is  therefore  clear.  These 
varieties  have  originated  by  loss  variations  or  loss  "mutations."  Is 
this  the  means  by  which  species  themselves  originate?  Many  biolo- 
gists have  recently  advocated  this  view,  as,  for  example,  Lotsy,  Baur, 
and  Bateson,  but  the  present  case  affords  rather  strong  evidence 
against  it.  The  color  varieties  of  guinea-pigs  differ  from  Cavia  rufescens 
and  C.  cutleri  (undoubtedly  distinct  species)  by  the  same  mendelizing 
color-factors,  but  there  is  no  evidence  that  these  two  species  differ  from 
each  other  by  any  color-factor.  The  two  wild  species  are  probably 
distinct  enough  to  show  interspecific  sterility,  since  one  is  known  to 
form  sterile  hybrids,  the  other  fertile  hybrids,  in  crosses  with  the 
guinea-pig.  Their  specific  distinctness  accordingly  can  not  be  due  to 
such  mendelizing  factors  as  distinguish  one  domesticated  variety  from 
another,  but  to  something  more  fundamental  in  character,  though  less 
striking  in  appearance. 


20  INHERITANCE    IN    GUINEA-PIGS. 


HYBRIDIZATION  EXPERIMENTS  WITH  A  RACE  OF  FERAL 
GUINEA-PIGS  FROM  ICA,  PERU. 

ORIGIN  AND  CHARACTERISTICS  OF  THE  ICA  RACE. 

Von  Tschudi  in  1844,  in  his  Fauna  of  Peru,  described,  under  the  name 
of  Cavia  cutleri,  a  wild  cavy  found  occurring  in  great  numbers  in  the 
state  of  lea.  He  says  that  the  natives  call  it  "cuy  del  monte,"  the 
mountain  cavy,  and  regard  it  as  the  original  of  C.  cobaye,  the  guinea-pig. 
Subsequent  writers  carefully  distinguish  the  C.  cutleri  of  Von  Tschudi 
from  that  of  Bennett,  with  which  my  wild  cavies  from  Arequipa  agree. 
One  of  the  objects  which  I  hoped  to  accomplish  by  the  trip  to  Peru  was 
to  learn  more  about  the  cavy  which  Von  Tschudi  reported  as  occur- 
ring at  lea,  and,  if  possible,  to  determine  its  relation  to  C.  cutleri  Bennett 
and  to  the  guinea-pig. 

Through  the  kindly  interest  of  Messrs.  W.  R.  Grace  &  Co.  I  was 
able  to  secure  3  wild-caught  cavies  (a  male  and  2  females)  from  lea 
and  to  bring  them  back  with  me  to  the  Bussey  Institution,  where  they 
have  produced  a  numerous  progeny. 

These  animals  were  about  the  size  of  domesticated  guinea-pigs,  were 
very  timid,  and  were  self-colored  golden  agouti,  in  every  respect  similar 
in  appearance  to  tame  guinea-pigs  of  the  color  variety  named. 

The  3  animals  brought  from  lea  produced  7  golden-agouti  young, 
all  similar  to  the  parents  in  color,  except  that  one  bore  a  spot  of  red, 
the  first  observed  indication  of  contamination  of  the  stock  with  char- 
acters found  in  domesticated  guinea-pigs.  That  other  indications 
were  not  observed  in  this  first  mating  of  the  animals  was  probably  due 
to  the  fact  that  the  male  was  homozygous  for  all  other  color  factors,  as 
subsequent  matings  of  the  females  with  a  son  of  one  of  them  by  the 
original  male  proved  that  both  mother  and  son  were  heterozygous  in 
that  variation  of  the  color  factor  which  is  seen  in  " red-eyed"  guinea- 
pigs  (Castle,  1914;  Wright,  1915).  The  same  matings  with  the  son 
(of  505,  table  12)  proved  that  one  of  the  two  original  females  (9503) 
was  also  heterozygous  in  the  agouti  factor  and  transmitted  white- 
spotting,  since  she  produced  a  black  daughter  which  had  one  white  foot. 
Three  other  inbred  descendants  of  the  original  trio  of  lea  animals  have 
also  borne  spots  of  white;  two  of  them  in  addition  bore  spots  of  red, 
and  so  were  tricolors.  One  of  the  original  trio  of  animals  from  lea 
(9502),  when  mated  with  of  505,  produced  a  son  (of  575)  which  was 
imperfectly  rough-coated.  Accordingly  we  have  clear  evidence  that 
the  stock  derived  from  lea  was  contaminated  with  at  least  5  of  the 
supposedly  independent  unit-factor  variations  which  occur  among 
domesticated  guinea-pigs  and  there  can  be  little  doubt  that  it  really  has 
been  derived  wholly  or  in  part  from  domesticated  guinea-pig  ancestors. 


GUINEA-PIGS   FROM   ICA.  21 

TABLE  12. — Young  produced  by  the  three  original  lea  guinea-pigs  or  their  inbred  descendants. 


A.  Both  parents  golden  agouti,  one  only  heterozygous  for  red-eye  (indicated  by  *). 


Father. 


Mother. 


Golden 
agouti 
young. 


Black 
young. 


501 
*505 
*505 
*505 
*533 

*533 


*502  and  *503 
509 
510 
530 
509 


One  young  with  spot  of  red. 


One  young  spotted  with  red  and  with 
white. 


625 


Total . 


24 


B.  Both  parents  golden  agouti  and  heterozygous  for  red-eye. 


Father. 


Mother. 


Golden 
agouti 
young. 


Silver 
agouti 
young. 


Black 
young. 


505 
505 
505 
505 
505 
533 
533 


502 
503 
504 
507 
605 
529 
540 


10 
9 
1 
8 
1 
5 
4 


One  slightly  rough. 

One  black  with  white  foot. 

One  spotted  with  red  and  with  white. 


One  spotted  with  white. 


Total . 


38 


18 


C.  Both  parents  silver  agouti  (red-eyed). 


Father. 


Mother. 


Silver 
agouti 
young. 


Father. 


Mother. 


Silver 
agouti 
young. 


565 
565 
565 
565 
565 
565 


527 
528 
573 
593 

601  and  604 
607 


569 
602 
798 
798 


587  and  588 
608 
701 
872 


Total . 


31 


The  question  at  once  arises  whether  the  stock  obtained  by  me  from 
lea  was  really  a  feral  stock,  in  origin  like  the  animals  described  by  Von 
Tschudi,  or  whether  they  were  present-day  domesticated  animals 
concerning  whose  origin  I  was  deceived.  Since  I  did  not  myself  see 
the  animals  captured  or  see  similar  animals  running  at  large  and  did 
not  even  visit  lea,  I  can  make  no  positive  statement  as  to  their  feral 
origin,  but  I  believe  the  report  made  to  me  by  the  agents  of  W.  R. 
Grace  &  Co.,  that  they  were  caught  feral  in  the  neighborhood  of  lea, 
to  be  correct  for  the  following  reasons:  (1)  The  animals  were  placed 


22 


INHERITANCE   IN   GUINEA-PIGS. 


on  board  our  steamer  during  a  stop  made  in  the  night  at  Pisco,  the 
terminus  of  the  short  line  of  railway  which  leads  down  from  lea  to  the 
coast.  I  found  them  the  next  morning  in  the  "butcher-shop,"  con- 
signed from  lea  to  W.  R.  Grace  &  Co.  in  Callao.  I  conclude  that  they 
really  did  come  from  the  neighborhood  of  lea.  (2)  I  saw  no  domesti- 
cated guinea-pigs  in  Peru  which  were  self-colored  like  these  animals. 
All  domesticated  ones  which  I  saw  in  Peru,  except  albinos,  were  spotted 
with  white,  or  with  yellow,  or  both.  Self  varieties  are  not  fancied  in 
Peru.  Varieties  of  this  sort  are  not  uncommon  among  the  guinea-pigs 
kept  by  European  and  American  fanciers,  but  apparently  they  have 
been  established  only  by  careful  and  long-continued  selection  from  the 
pied  stock  originally  introduced  from  South  America.  (3)  The  spotting 
and  the  rough  character  which  have  cropped  out  as  recessives  among 
the  descendants  of  the  three  lea  animals  are  feebly  expressed  characters 
which  appear  to  have  been  almost  obliterated,  but  which  still  come  to 
expression  feebly  under  inbreeding.  This  is  what  we  should  expect 
to  find  in  a  feral  race  acted  upon  by  natural  selection,  conspicuous 
variations  like  spotting  tending  to  disappear. 

TABLE  13.— Parentage  of  pure  lea  animals  whose  matings  are  recorded  in  table  12. 


Individual. 

Father. 

Mother. 

Individual. 

Father. 

Mother. 

Individual. 

Father. 

Mother. 

cfSOl1 

9527 

505 

507 

9601 

565 

527 

95021 

9528 

505 

503 

c?602 

565 

527 

95031 

9529 

505 

503 

9604 

505 

503 

9504 

501 

502  or  503 

9530 

505 

503 

9605 

505 

503 

d"505 

501 

502  or  503 

c?533 

505 

544 

9607 

565 

528 

9507 

501 

502 

9540 

505 

509 

9608 

565 

528 

9509 

501 

503 

c?565 

505 

507 

9625 

533 

509 

9510 

501 

503 

c?569 

505 

504 

9701 

565 

601  or  604 

9573 

505 

502 

c?798 

569 

587  or  588 

9587 

505 

507 

9827 

798 

701 

9588 

505 

507 

9593 

505 

504 

Original  stock. 

The  3  original  lea  animals  or  their  inbred  descendants  mated  inter  se 
have  produced  114  young,  of  which  62  have  been  golden  agoutis,  49  sil- 
ver agoutis,  and  3  blacks.;  4  of  the  114  have  shown  a  small  amount 
of  white  spotting,  3  have  shown  yellow  spotting,  and  1  has  shown  a 
small  amount  of  roughness  of  the  coat. 

The  various  matings  which  have  produced  these  young  are  classified 
in  three  groups  in  table  12,  and  the  parentage  of  each  animal  which 
took  part  in  a  mating  is  shown  in  table  13,  from  which  pedigrees  may 
readily  be  drawn  tracing  back  to  the  original  trio.  It  will  be  observed 
from  table  12  that  silver  agouti  was  derived  from  golden  agouti  as  a 
recessive  and  has  bred  true  without  exception  (31  silver  agouti  young 
being  produced  by  silver  agouti  parents). 


GUINEA-PIGS   FROM   ICA. 


23 


CROSSES  BETWEEN  THE  ICA  RACE  AND  GUINEA-PIGS  OF  RACE  C. 

An  albino  male  guinea-pig  (d"54)  of  race  C  was  mated  with  5  golden 
agouti  females  of  the  lea  stock.  It  was  hoped  from  this  cross  to  learn 
as  promptly  as  possible  the  gametic  composition  of  the  lea  race,  since 
race  C  contained  a  larger  number  of  recessive  Mendelian  factors  than 
any  other  race  in  the  laboratory.  In  this  hope  we  were  not  disap- 
pointed. Race  C  has  already  been  described.  It  contains  two  different 
recessive  variations  of  the  color  factor,  dilution  and  albinism,  which  are 
allelomorphic  with  each  other  and  with  ordinary  color,  thus  forming  a 
system  of  triple  allelomorphs,  C,  Cd,  and  Ca,  with  dominance  in  the 
order  named  (see  Wright,  1915).  It  lacks  agouti,  black,  and  extension 
factors.  Visibly  the  animals  of  this  race  are  either  brown-eyed  cream 
or  albino.  Male  54  was  an  albino,  bearing  the  color  allelomorph  Ca, 
which  is  recessive  to  the  color  allelomorph  Cd  found  in  brown-eyed 
cream  individuals  of  race  C.  The  mating  between  d"  54  and  the  5  golden 
agouti  females  of  the  lea  race  produced  13  young,  7  of  which  were 

TABLE  14. — Fi  result  of  mating  the  albino  <?54  of  race  C  with  golden  agouti 
females  of  the  lea  race. 


Dark-eyed 

Red-eyed  young. 

Mother. 

young. 
Golden 
agouti. 

Silver 
agouti. 

Sepia. 

502 

3 

1 

503 

1 

1 

1 

504 

2 

507 

1 

1 

509 

2 

Total  .  .  . 

7 

3 

3 

golden  agouti  (like  the  mothers),  3  silver  agouti,  and  3  a  dull  black  or 
slate  color,  which  will  be  called  sepia.  The  silver  agouti  young  were 
like  those  produced  by  lea  animals  bred  inter  se.  The  sepia  young 
represented  a  new  class  not  previously  observed.  In  common  with  the 
silver  agoutis  they  had  no  yellow  in  their  fur.  The  ticking  and  spotting 
of  silver  agoutis  was  of  white,  as  was  also  the  spotting  of  the  sepias, 
which  had  no  ticking.  It  seemed  probable,  therefore,  as  proved  to  be 
the  case,  that  the  silver  agouti  and  the  sepia  young  differed  from  each 
other  only  in  the  presence  or  absence  of  the  agouti  factor.  But  these 
two  classes  of  young  taken  together  differ  from  golden  agoutis  in  lacking 
yellow  pigmentation  with  which  the  golden  agouti  fur  is  ticked.  They 
also  differ  from  golden  agoutis  in  the  intensity  of  the  eye  pigmentation, 
which  is  very  great  in  golden  agoutis  and  blacks,  but  ordinarily  shows 
such  reduction  in  silver  agoutis  and  sepias  that  the  eye  by  reflected  light 
has  a  deep  red  glow.  It  will  be  convenient  to  distinguish  them  as  red- 


24  INHERITANCE    IN   GUINEA-PIGS. 

eyed,  it  being  understood  that  the  red  eye  is  invariably  associated  with 
no-yellow  in  the  coat. 

Four  of  the  five  lea  mothers  which  were  mated  with  d"54  had  pro- 
duced silver  agouti  (red-eyed)  young  by  lea  mates.  Each  of  them 
produced  red-eyed  young  by  c?54;  together  they  produced  5  dark-eyed 
young  (golden  agouti)  and  6  red-eyed  (silver  agouti  or  sepia).  The 
fifth  lea  mother  (9509)  had  produced  11  golden  agouti  young  when 
mated  with  lea  males  known  to  be  heterozygous  for  silver  agouti. 
(See  table  12.)  This  is  good  evidence  that  she  did  not  carry  red-eye  as 
a  recessive  character  and  was  accordingly  homozygous  for  dark-eye. 
By  d"54  she  produced  2  golden  agouti  young. 

From  these  several  facts  it  appears  that  dark-eyed  lea  animals 
capable  of  producing  red-eyed  young  when  mated  inter  se,  produce  equal 
numbers  of  dark-eyed  and  red-eyed  young  when  mated  to  albinos,  but 
produce  no  albinos.  This  indicates  that  albinism  is  recessive  both  to 
red-eye  and  dark-eye,  an  indication  which  the  F2  result  confirms.  It 
will  be  shown  further  that  the  three  conditions  are  mutually  allelomor- 
phic,  so  that  a  zygote  may  contain  any  two  of  the  three,  but  not  more. 
Red-eye  is  in  fact  a  fourth  member  of  the  albino  series  of  allelomorphs, 
which  includes  the  following  conditions  in  order  of  dominance :  (1)  ordi- 
nary dark-eye  and  colored  coat,  such  as  is  seen  in  Cavia  cutleri  and  in 
golden  agouti  animals  of  the  lea  race;  (2)  dark-eye  with  dilute  coat, 
seen  in  colored  animals  of  race  C;  (3)  red-eye  and  non-yellow  coat; 
(4)  albino.  (See  Wright,  1915.)  For  convenience  these  allelomorphs 
may  be  designated  by  C,  Cd,  Cr,  and  Ca.  The  cross  of  lea  females 
with  the  albino  cf  54  involves  animals  of  the  formulae  CC  or  CCr  mated 
with  an  animal  of  the  formula  CaCa.  The  7  golden  agouti  young  are 
expected  to  be  of  the  formula  CCa;  the  6  red-eyed  young  of  the 
formula  CrCa.  We  may  now  compare  the  experimental  with  the 
expected  results  of  breeding  such  animals  in  various  ways. 

THE  F2  GENERATION. 

One  of  the  F!  silver  agouti  males  (c?517)  was  known  from  his  pedi- 
gree to  be  heterozygous  hi  four  characters,  viz,  red-eye  vs.  albinism, 
agouti  vs.  non-agouti,  black  vs.  brown,  and  extension  vs.  restriction. 
His  formula  was  accordingly  CrCaAaBbEe,  and  we  should  expect  him 
to  form  gametes  of  16  different  sorts,  all  equally  numerous.  This 
animal  was  mated  with  all  three  kinds  of  F!  females,  with  the  results 
shown  in  table  15.  The  golden  agouti  females  produced  25  young, 
distributed  among  10  classes  very  distinctly  different  in  appearance. 
These  golden  agouti  females  were  known  from  pedigree  to  be  hetero- 
zygous for  the  same  4  factors  as  cf  517,  but  to  contain  a  different  allelo- 
morph for  albinism.  Both  he  and  they  carried  albinism  as  a  recessive 
character,  but  whereas  he  carried  red-eye  (Cr)  as  its  dominant  allelo- 
morph, they  carried  dark-eye  (the  ordinary  condition  of  the  color 


GUINEA-PIGS   FROM   ICA. 


25 


factor,  viz,  C).  His  gametes  accordingly  could  transmit  either  Cr  or 
Ca,  but  theirs  would  transmit  either  C  or  Ca.  Accordingly  their  young 
should  be  in  the  ratio  2  dark-eyed  to  1  red-eyed  to  1  albino.  The  observed 
numbers  were  13:8:4.  Each  of  these  three  groups  might  theoretically 
contain  8  different  kinds  of  individuals,  but  certain  of  these  would  be 
visibly  indistinguishable.  The  classes  visibly  different  which  might 
themselves  be  expected  to  be  composite  are  black-eyed  reds  and  brown- 

TABLE  15. — Fi  young  from  the  cross  <?54  albino  (race  C)X  golden  agouti  females  of  lea  race. 


Parents. 

Dark-eyed  young. 

Golden 
agouti. 

Black. 

Cinna- 
mon. 

Choco- 
late. 

Black- 
eyed 
red. 

Brown- 
eyed 
red. 

c?517  silver  agouti  X  9  golden  agouti.  .  .  . 
Expected  

6 
5.3 

1 

1.8 

2 
1.8 

0 
0.6 

2 
2.3 

2 
0.8 

c?517  silver  agouti  X  9  silver  agouti  

Expected  

cT517  silver  agouti  X  9  sepia  

Expected  

Total  observed  

6 
5.3 

1 

1.8 

2 
1.8 

0 
0.6 

2 
2.3 

2 
0.8 

Total  expected  

Parents. 

Red-eyed  young. 

Albinc 
young 

'  Total. 

Silver 
agouti. 

Sepia. 

Silver 
cinna- 
mon. 

Red- 
eyed 
choco- 
late. 

Red- 
eyed 
white. 

c?517  silver  agouti  X  9  golden  agouti  
Expected  

3 
2.6 

2 
0.9 

2 
0.9 

1 
0.3 

0 
1.5 

4 
6.3 

25 

c?517  silver  agouti  X  9  silver  agouti  
Expected  

0 

2.8 

1 
0.9 

1 
0.9 

0 
0.3 

4 
1.7 

3 
2.3 

9 

c?517  silver  agouti  X  9  sepia  

5 

7.4 

5 

7.4 

1 
2.4 

1 
2.4 

8 
6.5 

15 

8.7 

35 

Expected  

Total  observed  

8 
12.8 

8 
9.2 

4 
4.2 

2 
3.0 

12 

9.7 

22 
17.3 

69 

Total  expected  

eyed  reds,  each  of  which  might  include  both  agouti  and  non-agouti 
animals;  also  red-eyed  whites,  which  might  have  either  black  or  brown 
pigment  in  the  reddish  eye,  and  might  transmit  either  agouti  or  non- 
agouti;  and  finally,  the  albinos,  which  might  be  of  as  many  different 
sorts  as  the  colored  classes,  viz,  16. 

All  except  2  of  the  12  visibly  different  classes  expected  from  this 
mating  were  obtained  in  as  small  a  total  number  of  young  as  25.  In 
the  two  missing  classes,  chocolate  and  red-eyed  white,  the  theoretical 


26 


INHERITANCE    IN   GUINEA-PIGS. 


numbers  were  only  0.6  and  1.5  individuals  respectively,  so  that  their 
absence  was  not  surprising. 

By  silver  agouti  Fx  females,  c?517  had  9  young  of  4  different  color 
varieties,  the  maximum  number  of  classes  expected  being  6. 

By  sepia  F!  females,  cf517  had  35  young,  distributed  among  6  dif- 
ferent color  classes,  as  expected.  Summarizing  the  results  from  all 
three  lands  of  matings,  we  find  that  the  F2  young  of  d"517  number  69, 
distributed  among  11  of  the  12  expected  classes  of  young,  the  missing 
class  being  one  in  which  the  expectation  is  for  0.6  of  an  individual, 
scarcely  more  than  an  even  chance  for  the  production  of  such  an  indi- 
vidual in  the  number  of  young  recorded.  (See  table  15.) 

TABLE  16. — Young  produced  by  red-eyed  white  parents  mated  inter  se. 


Father. 

Mother. 

Red-eyed 
white 

Albino 

young. 

young. 

567 

571 

2 

1 

576 

726 

10 

0 

774 

747 

5 

2 

774 

758 

3 

3 

774 

775 

8 

0 

842 

571 

2 

0 

849 

851 

2 

0 

T< 

ital  

32 

6 

A  word  as  to  the  number  of  classes  expected  may  not  be  out  of  place. 
The  dark-eyed  classes  expected  are  6,  identical  with  those  expected 
from  the  cross  of  race  C  animals  with  wild  Cavia  cutleri.  (Compare 
p.  16.)  The  number  of  classes  expected  among  the  red-eyed  young  is 
1  less,  namely  5,  because  red-eyed  whites  which  have  brown  pigment 
in  the  eye  can  not  be  distinguished  (except  by  breeding-test  or  post 
mortem)  from  those  which  have  black  pigment  in  the  eye,  the  quantity 
of  pigment  present  being  too  small,  and  the  coat  in  both  cases  white. 

On  the  whole  the  agreement  between  expected  and  observed  in  this 
experiment  is  so  good  as  to  preclude  the  idea  that  any  coupling  or 
association  occurs  among  the  4  unit  factors  involved  in  the  cross. 

This  experiment  produced  4  color  varieties  of  guinea-pig  previously 
unknown  to  me,  viz,  the  4  red-eyed  classes  other  than  silver  agoutis, 
which  had  already  been  obtained  from  the  uncrossed  lea  race.  (See 
plates  1,  2,  and  5.)  The  eye  has  a  similar  appearance  in  all  the  red- 
eyed  classes,  showing  a  deep-red  glow  by  reflected  light.  The  silver 
agouti  variety,  as  already  explained,  differs  from  golden  agouti  in  the 
ticking  of  the  fur,  which  is  white  in  silver  agouti,  instead  of  red  or 
yellow  as  in  golden  agouti.  Sepia  as  compared  with  black  has  a  more 
faded  appearance,  approaching  chocolate  on  the  sides  of  ,the  body  and 
belly,  but  always  darker  and  unmistakably  black  above.  Silver  china- 


GUINEA-PIGS   FROM   ICA. 


27 


mon  (or  "red-eyed  cinnamon/'  plate  5,  fig.  31)  differs  from  silver  agouti 
in  having  brown  hairs  ticked  with  white  instead  of  black  hairs  ticked 
with  white.  It  is  one  of  the  handsomest  of  guinea-pig  varieties.  Red- 
eyed  chocolate  is  indistinguishable  from  dark-eyed  chocolate,  except  in 
eye  color.  The  red-eyed  whites  all  look  alike,  though  they  may  differ 
considerably  in  factorial  composition.  Their  production  in  this  experi- 
ment was  a  complete  surprise  to  us  and  very  puzzling  until  the  sugges- 
tion was  made  (I  think  by  Mr.  Wright)  that  an  essential  feature  of 
the  red-eyed  variation  was  the  absence  of  yellow  color  from  the  fur. 
It  was  then  realized  that  a  " yellow"  animal  with  red  eyes  and  " non- 
yellow"  fur  must  of  necessity  have  white  fur.  This  suggestion  was 
immediately  put  to  the  test  by  mating  the  red-eyed  white  c?576  with 
3  dark-eyed  cream  females.  They  produced  12  young,  of  which  5  were 
brown-eyed  cream,  2  black-eyed  cream,  3  red-eyed  white,  and  2  albino. 
No  young  were  produced  which  had  coats  of  any  other  color  than 
yellow!  Hence  it  is  clear  that  red-eyed  whites  do  not  transmit  the 
extension  factor.1 

TABLE  17. — Results  of  mating  red-eyed  white  individuals  with  albinos. 


Red-eyed  young. 

Father, 

Mother, 

Albino 

red-eyed. 

albino. 

Silver 
agouti. 

Sepia. 

Silver 
cinnamon. 

Choco- 
late. 

White. 

young. 

567 

564 

4 

4 

567 

568 

1 

2 

567 

572 

1 

1 

1 

2 

567 

177 

1 

567 

711 

2 

7 

576 

1430 

1 

1 

576 

1439 

1 

1 

576 

1446 

1 

2 

T 

otal  

3 

3 

1 

2 

5 

19 

This  same  red-eyed  white  c?576  was  also  mated  with  3  albino 
females  of  race  B,  which  carry  the  extension  factor.  Both  parents, 
it  will  be  observed,  were  white,  one  having  red  eyes,  the  other  pink  eyes. 
This  mating  produced  7  young,  of  which  3  were  red-eyed  with  silver- 
agouti-colored  coats  and  4  were  albinos.  The  production  of  colored 
young  in  this  case  shows  that  red-eyed  white  animals  may  transmit  all 
that  is  necessary  for  the  production  of  a  colored  coat  except  the  exten- 
sion factor,  which  the  albino  parents  supplied. 

The  red-eyed  white  cf  576  was  evidently  heterozygous  for  the  black 
factor,  since,  when  he  was  mated  with  brown-eyed  cream  females,  he 
produced  both  black-eyed  and  brown-eyed  cream  young.  Another 


JAs  a  further  test  of  red-eyed  whites,  two  other  red-eyed  white  males  (615  and  616)  were  mated 
with  several  different  red  or  yellow  coated  females.  They  produced  9  red  or  yellow  young,  5  red- 
eyed  young,  and  5  albino  young,  a  result  completely  in  accord  with  that  given  by  d"1  576. 


28 


INHERITANCE   IN   GUINEA-PIGS. 


red-eyed  white  male,  567,  an  F3  descendant  of  the  albino  cf  54,  race  C, 
was  found  to  be  homozygous  for  brown  (table  17).  What  pigment  his 
eyes  contained  was  undoubtedly  brown,  for  when  he  was  mated  with  3 
albino  females  descended  from  the  albino  cf  54,  race  C,  he  produced  1 
silver  cinnamon  and  2  red-eyed  chocolate  young,  besides  5  red-eyed 
white  and  8  albino  young.  The  entire  absence  of  black-colored  young 
indicates  that  this  male,  as  well  as  his  albino  mates,  transmitted  the 
capacity  to  form  brown  but  not  black  pigmentation.  When,  however, 
this  same  male  (567)  was  mated  with  an  albino  derived  from  race  B, 
which  never  produces  brown  individuals,  there  were  obtained  3  sepia- 
colored  young  with  red  eyes,  besides  7  albinos,  showing  that  when  the 
mother  transmitted  black,  this  male  produced  black-pigmented  young, 
black  being  dominant  over  brown  which  he  himself  transmitted. 

TABLE  18. — Results  of  mating  a  red-eyed  white  male  with  brown-eyed  cream  females. 


Young. 

Black-eyed 
cream. 

Brown-eyed 
cream. 

Red-eyed 
white. 

Albino. 

576 

-46 

2 

1 

2 

576 

M250 

1 

1 

576 

762 

1 

2 

2 

842 

870 

1 

1 

Tot 

al  

2 

6 

3 

3 

Both  the  males  whose  matings  have  just  been  described,  viz,  567  and 
576,  were  heterozygous  in  albinism,  since  when  mated  with  albinos  they 
produced  about  50  per  cent  of  albino  young.  They  were  evidently  of 
the  formula  CrCa.  If  red-eyed  white  animals  of  this  formula  should 
be  mated  with  each  other  we  should  expect  individuals  to  be  produced 
which  are  homozygous  for  red-eye,  i.  e.,  are  of  formula  CrCr.  Two 
probably  homozygous  red-eyed  females  of  this  sort  have  been  discov- 
ered in  mating  red-eyed  white  animals  inter  se.  One  of  them  (9  726, 
table  16)  produced  10  young,  all  red-eyed  white,  in  matings  with  cf576, 
known  to  be  heterozygous  for  albinism.  Had  this  female  formed 
albino  gametes  she  should  have  produced  25  per  cent  of  albino  young 
in  the  matings  mentioned.  It  seems  probable,  therefore,  that  she  did 
not  form  such  gametes.  The  F3  9  775  (table  16)  was  probably  like- 
wise homozygous,  since  her  mate  is  known  to  have  been  heterozygous 
for  albinism,  but  she  produced  no  albinos  in  a  total  of  8  young. 

In  the  foregoing  account  nothing  has  been  said  concerning  spotting 
with  white  or  with  yellow;  nevertheless  spotting  of  both  sorts  occurred 
among  certain  of  the  FI  and  F2  young  obtained  from  the  lea  crosses. 
Since  the  uncrossed  lea  race  contained  spotted  animals  of  both  sorts,  it 
is  not  surprising  that  the  cross-bred  descendants  of  this  race  should 


GUINEA-PIGS   FROM   ICA.  29 

do  the  same.  Race  C,  like  the  lea  race,  contains  only  an  occasional 
individual  sparingly  spotted  with  white;  yellow  spotting  is  of  course 
not  visible  in  a  race  like  C,  which  contains  only  yellow  or  albino  indi- 
viduals. It  will  suffice  to  say  that  the  cross-breds,  like  the  parent  races, 
consisted  principally  of  self-colored  individuals,  and  that  only  an  occa- 
sional dark-eyed  individual  bore  white  markings,  which  in  no  case  were 
extensive,  but  were  usually  limited  to  a  white  foot.  Among  the  red- 
eyed  individuals,  white  spotting  was  commoner  and  more  extensive, 
which  might  seem  surprising,  unless  one  remembers  that  in  red-eyed 
individuals  it  is  impossible  to  distinguish  true  white  spotting  from 
yellow  spotting,  since  both  produce  uncolored  areas  in  the  coat.  Com- 
plications of  this  nature  make  this  cross  unfavorable  for  the  study  of 
the  inheritance  of  spotting. 

SUMMARY  ON  THE  ICA  RACE. 

1.  The  "lea  race"  of  guinea-pigs  consists  of  descendants  of  1  male 
and  2  female  golden  agoutis  obtained  from  the  vicinity  of  lea,  Peru, 
in  1911,  and  reported  to  have  been  caught  wild.     These  animals  are 
supposed  to  have  been  descendants  of  guinea-pigs  long  since  escaped 
from  domestication. 

2.  This  explanation  is  supported  by  the  observation  that  within  the 
lea  race  have  cropped  out  5  Mendelian  variations  which  are  common 
among  domesticated  guinea-pigs,  viz,  (1)  the  "red-eye"  variation,  one  of 
the  four  allelomorphic  forms  of  the  color  factor  in  guinea-pigs;  (2)  the 
"non-agouti"  allelomorph  of  the  agouti  factor;  (3)  the  factor  which 
produces  rough  coat;  (4)  the  factor  for  white  spotting;  and  (5)  the 
factor  for  yellow  spotting. 

3.  An  albino  guinea-pig  of  race  C  differing  from  wild  guinea-pigs  by 
4  recessive   Mendelian  characters   was  crossed  with  golden  agouti 
females  of  the  lea  race.    From  this  cross  were  obtained  in  F2  all  except 
one  of  the  expected  recombinations  of  the  4  unit-factor  differences 
between  the  races  crossed.     Leaving  out  of  consideration  spotting 
with  white  and  with  red,  which  occurred  among  some  of  the  hybrids  as 
well  as  in  the  uncrossed  lea  race,  there  occurred  5  easily  distinguishable 
classes  of  dark-eyed  young  and  5  classes  of  red-eyed  young,  besides 
albinos.     Only  one  "expected"  class  of  F2  young  was  missing,  the 
occurrence  of  which  among  other  races  is  well  known.    There  is  almost 
an  even  chance  for  its  failure  to  appear  in  this  experiment  in  the  number 
of  young  recorded. 

4.  The  four  color  factors  involved  in  the  cross  and  their  allelomorphs 
are: 

A,  a     =  agouti,  non-agouti; 

B,  b     =  black,  brown; 

C,  Cr   =  full  color,  red-eye; 

E,  e     =  extension  (of  black  or  brown),  restriction. 


30  INHERITANCE    IN   GUINEA-PIGS. 

These  are  capable  theoretically  of  forming  16  different  combinations, 
as  follows,  heterozygous  combinations  being  omitted.  The  appearance 
of  zygotes  containing  each  of  these  several  combinations  is  indicated 
opposite  the  respective  combinations. 

ABCE,  golden  agouti  =  wild  type. 
Single  mutations. 


ABCe,      black-eyed  red. 
ABCrE,   silver  agouti. 


AbCE,     cinnamon. 
aBCE,     black. 


Double  mutations. 


ABCre, 
AbCrE, 
abCE, 

red-eyed  white, 
silver  cinnamon, 
chocolate. 

AbCe, 
aBCrE, 
aBCe, 

brown-eyed  red. 
red-eyed  sepia, 
black-eyed  red 

Triple  mutations. 

AbCre, 
aBCre, 

red-eyed  white, 
red-eyed  white. 

abCe, 
abCrE, 

brown-eyed  red. 
red-eyed  chocolate. 

Quadruple  mutation. 
abCre,  red-eyed  white. 

Of  the  16  different  combinations,  2  produce  black-eyed  red  individuals 
indistinguishable  except  by  breeding  test;  the  same  is  true  regarding 
brown-eyed  reds.  Four  other  combinations  identical  with  these,  except 
for  the  substitution  of  Cr  for  C,  produce  red-eyed  whites,  which  visibly 
are  all  alike  but  which  breed  differently.  Three  of  the  four  kinds  of 
red-eyed  whites  have  been  identified  by  breeding  test;  no  doubt  the 
fourth  can  easily  be  obtained.  The  fact  that  the  several  classes  of 
red-eyed  whites  look  alike,  and  that  the  two  kinds  of  black-eyed  reds 
look  alike,  and  further,  that  the  two  kinds  of  brown-eyed  reds  look 
alike,  reduces  the  number  of  visibly  distinguishable  classes  from  16  to 
11,  all  except  one  of  which  have  been  recorded  from  this  single  experi- 
ment. The  experiment  also  produced  albinos  which  theoretically 
should  be  of  8  different  formulae,  if  in  the  formula  Ca  is  everywhere 
substituted  for  its  allelomorphs  C  or  Cr.  No  attempt  has  been  made 
to  distinguish  the  several  expected  classes  of  albinos  by  breeding  tests, 
the  only  certain  means  of  identifying  them. 

5.  The  close  agreement  observed  between  theoretical  and  recorded 
numbers  of  F2  offspring  in  this  cross  lends  no  support  to  the  idea  that 
any  association  or  linkage  occurs  among  the  4  factorial  variations 
involved. 


GUINEA-PIGS   FROM   AREQUIPA.  31 

HYBRIDIZATION  EXPERIMENTS  WITH  A  DOMESTICATED 
GUINEA-PIG  FROM  AREQUIPA. 

While  in  Arequipa,  in  December  1911, 1  purchased  in  the  cabin  of  a 
native  living  near  the  observatory  a  pair  of  domesticated  guinea-pigs 
about  one-third  grown  and  perhaps  2  or  3  months  old.  These  animals 
resembled  the  ordinary  pied  guinea-pigs  kept  for  pets  or  laboratory  use 
in  Europe  and  North  America.  The  female  was  a  tricolor,  red,  white, 
and  black,  and  was  rough-coated  of  grade  B  (Castle,  1905,  p.  57).  The 
male  was  a  dilute-pigmented,  agouti-marked  tricolor  (yellow  agouti,1 
cream,  and  white),  and  smooth-coated.  This  pair  of  animals  was  suc- 
cessfully transported  to  the  Bussey  Institution,  where  they  produced 
3  litters,  of  1,  3,  and  2  young  respectively.  The  young  of  the  first 
2  litters  died  at  birth;  the  third  litter  consisted  of  2  males,  and  as 
the  mother  died  soon  afterward  it  was  impossible  to  propagate  the 
family  farther  for  lack  of  females.  Of  the  6  young  produced,  3  were 
rough-coated  and  3  smooth,  showing  the  mother  to  have  been  hetero- 
zygous for  rough  coat,  a  dominant  character  (Castle,  1905).  Three 
were  golden  agouti  and  white  and  three  tricolor,  one  being  golden 
agouti  red  and  white,  the  other  two  silver  agouti  yellow  and  white. 

MALE  1002  AND  HIS  F,  OFFSPRING. 

The  father  of  this  family  of  guinea-pigs  (cfl002)  proved  to  be  an 
animal  of  great  vigor  and  vitality.  Although  born  in  Peru  (about 
September  1911)  and  brought  to  North  America  in  mid-winter,  he  has 
successfully  escaped  the  ravages  of  disease  among  our  guinea-pigs 
throughout  the  rigors  of  four  New  England  winters  and  is  still  vigorous 
and  active.  In  crosses  with  other  races  of  guinea-pigs  he  has  sired 
several  hundred  young  and  is  now  being  mated  with  females  which  are 
simultaneously  his  daughters,  his  granddaughters,  and  his  great- 
granddaughters!  By  repeated  back-crosses  such  as  these  a  race  has 
been  established  which  derives  its  inherited  characters  largely  from 
this  one  animal.  This  race  will  be  designated  the  "Arequipa"  race. 

Crosses  of  cf  1002  and  repeated  back-crosses  with  his  female  descen- 
dants have  permitted  a  very  full  analysis  of  the  factorial  constitution 
of  this  animal.  He  possesses  either  as  dominant  or  as  recessive  char- 
acters a  majority  of  the  Mendelian  variations  of  guinea-pigs,  including 
one  not  previously  known  to  occur  in  any  animal  other  than  mice,  viz, 

JIt  should  be  noted  that  "silver  agoutis"  may  be  of  two  different  sorts:  (1)  dark-eyed  silver 
agouti  with  cream-colored  hair-tips,  and  (2)  red-eyed  silver  agouti  with  white  hair-tips.  The  two 
varieties  resemble  each  other  somewhat  and  it  often  requires  close  observation  to  discriminate 
between  them,  but  genetically  they  are  quite  distinct.  Only  the  former  sort  was  known  to  me 
previous  to  the  Peruvian  expedition,  and  the  term  "silver  agouti"  as  used  in  my  1905  paper  and 
by  fanciers  generally  refers  to  this.  It  would  be  better,  I  think,  to  use  the  term  cream  agouti  or 
yellow  agouti  for  such  agouti  animals  as  develop  pale  yellow  in  the  fur  and  to  restrict  the  term 
silver  agouti  to  those  which  are  non-yellow. 


32 


INHERITANCE   IN   GUINEA-PIGS. 


the  pink-eye  variation  with  colored  coat,  first  brought  to  the  attention 
of  scientists  in  the  case  of  mice  through  the  experiments  of  Darbishire 
(1902).  A  similar  variation  has,  however,  since  been  found  to  occur 
in  rats  (Castle,  1914) .  The  number  of  factors  in  which  d1 1002  is  hetero- 
zygous is  surprisingly  large  and  implies  doubtless  considerable  cross- 
breeding in  the  guinea-pig  colonies  kept  by  the  natives  of  Arequipa,  a 
fact  perhaps  connected  with  the  great  size  and  vigor  of  their  animals. 
The  factorial  constitution  of  cfl002,  as  at  present  understood,  is  as 
follows: 

(1)  Agouti  factor,  Aa,  agouti-marked  but  transmitting  non-agouti  as  a  recessive 

character. 

(2)  Black  factor,  BB,  homozygous. 

(3)  Color  factor,  CaCr,  two  different  recessive  variations,  dilution  (Cd)  being 

dominant  over  red-eye  (Cr).  Both  are  recessive  to  ordinary  intense  color 
(C)  and  dominant  over  albinism  (Ca),  the  four  forming  a  series  of  quadruple 
allelomorphs,  as  shown  by  Wright  (1915). 

(4)  Extension  factor,  EE,  homozygous. 

(5)  Dark-eye  factor,  Pp,  heterozygous  for  the  recessive  pink-eye  (p)  variation, 

with  which  goes  dilution  of  black  or  brown  pigments,  but  not  of  yellow. 

(6)  As  regards  the  rough  variation,  this  animal  is  smooth,  but  nevertheless  trans- 

mits occasionally  a  trace  of  the  rough  character,  but  the  character  does  not 
crop  out  among  his  descendants  in  any  as  yet  recognizable  Mendelian 
proportions. 

(7)  White  spotting,  homozygous. 

(8)  Yellow  spotting,  homozygous. 

TABLE  19. — Classification  of  young  obtained  from  matings  of  &1002  with  unrelated  guinea-pigs. 


Mothers. 

Intense  dark-eyed. 

Dilute  dark-eyed. 

Red-eyed. 

Golden 
agouti. 

Black. 

Yellow 
agouti. 

Sepia. 

Silver 
agouti. 

Sepia. 

5  dark-eyed  non-agoutis  

4 
16 

7 
8 

2 

6 
2 

2 

2 
5 

17 
9 

6 
2 

15  dark-eyed  non-agoutis,  heter- 
ozygous for  albinism  

6  albinos  

Total  

20 

15 

10 

9 

26 

8 

Male  1002  was  mated  with  20  dark-eyed  guinea-pigs  and  6  albinos 
derived  either  from  race  B,  from  a  4-toed  race  (see  Castle,  1906),  or 
from  crosses  between  the  two.  Both  these  races  contain  only  non- 
agouti  animals.  The  dark-eyed  mothers  produced  70  FI  young,  the 
albino  mothers  produced  18  F!  young.  Disregarding  spotting  with 
yellow  and  with  white,  the  young  of  the  dark-eyed  mothers  fall  into 
three  classes — dark-eyed  intense,  dark-eyed  dilute,  and  red-eyed — and 
each  class  may  be  further  subdivided  into  agouti  and  non-agouti.  (See 
table  19.) 

The  albino  mothers,  though  derived  from  the  same  races  as  the  dark- 
eyed  mother,  produced  only  two  of  the  three  main  classes  of  young, 
viz,  dark-eyed  dilute  and  red-eyed,  which  fact  confirms  Wright's  (1915) 


GUINEA-PIGS   FROM   AREQUIPA.  33 

conclusion  that  albinos,  even  when  derived  from  intense  dark-eyed 
parents,  do  not  transmit  intensity  to  their  young  in  crosses,  for  the 
reason  that  albinism  is  an  allelomorph  of  dilution  as  well  as  of  intensity. 
The  fact  that  d"  1002  produced  no  albino  young,  even  when  mated  with 
albinos,  shows  that  he  did  not  produce  albino  gametes.  The  fact  that 
he  produced  red-eyed  young  when  mated  with  albinos  shows  that  he 
transmitted  red-eye  as  a  recessive  character  and  that  this  is  dominant 
over  albinism.  The  fact  that  he  produced  no  intense  dark-eyed  young 
by  the  albino  mothers  shows  that  he  lacks  intensity  and  forms  only 
gametes  which  transmit  either  dilution  or  red-eye.  All  these  facts  are 
in  harmony  with  the  hypothesis  suggested  by  Wright  (1915)  that  inten- 
sity, dilution,  red-eye,  and  albinism  are  allelomorphs  of  each  other,  so 
that  a  gamete  can  transmit  only  one  of  the  four  allelomorphs,  and  a 
zygote  can  contain  only  two  of  them.  Male  1002  is  evidently  a  hetero- 
zygote  of  dilution  and  red-eye  (CdCr),  both  of  which  are  recessive  to 
intensity  (C)  and  dominant  over  albinism  (Ca).  Consequently,  when 
he  is  crossed  with  albinos,  zygotes  of  two  sorts  are  expected  in  equal 
numbers,  viz,  CdCa  and  CrCa  (dilute  and  red-eyed),  as  observed  (table 
19) ;  and  when  he  is  crossed  with  intense  dark-eyed  animals  carrying 
albinism  as  a  recessive  character  (as  15  of  the  20  dark-eyed  mothers  of 
table  19  did),  zygotes  of  four  sorts  are  expected  in  equal  numbers,  viz, 
CCd,  CCr,  CdCa,  and  CrCa,  the  first  two  being  dark-eyed  intense,  the 
third  dark-eyed  dilute,  and  the  fourth  red-eyed.  The  observed  result 
is  in  perfect  accord  with  this  expectation  as  regards  the  classes  of  young 
produced,  and  agrees  with  expectation  sufficiently  well  as  regards  the 
proportions  of  the  classes. 

It  is  expected  further  that  each  of  the  three  main  classes  will  be  sub- 
divided about  equally  into  agoutis  and  non-agoutis.  The  6  expected 
subclasses  appear  in  the  experimental  results,  but  there  is  a  considerable 
excess  of  agoutis,  viz,  56  agoutis  to  32  non-agoutis.  Whether  this  depar- 
ture from  the  expected  equality  has  any  probable  significance  will  be 
considered  further  in  connection  with  the  F2  generation. 

F2  OFFSPRING  OF  cflOOl 

For  the  production  of  an  Fa  generation  a  golden  agouti  and  4  silver 
agouti  males  were  selected.  The  golden  agouti  male  was  mated  only 
with  a  black  female,  his  sister,  but  the  silver  agouti  males  were  mated 
with  practically  all  classes  of  the  Fx  females.  (See  table  20.)  They 
produced  altogether  190  F2  young,  which,  being  classified  as  regards 
intensity  and  eye  color  alone,  fall  into  6  main  classes,  viz,  (1)  dark-eyed 
intense,  (2)  dark-eyed  dilute,  (3)  red-eyed,  (4)  pink-eyed,  (5)  red-and- 
pink-eyed,1  and  (6)  albino.  Each  of  these  main  groups  falls  into  two 

1  Animals  called  red-and-pink-eyed  are  in  reality  pink-eyed,  but  lack  yellow  in  the  coat.     They 
transmit  in  every  gamete  both  the  factor  for  pink-eye  and  the  factor  for  red-eye. 


34 


INHERITANCE   IN    GUINEA-PIGS. 


subclasses  (agouti  and  non-agouti),  readily  distinguishable,  except  in 
the  case  of  albinos. 

Matings  in  which  both  parents  were  agoutis  produced  44  agouti  to 
13  non-agouti  young,  expected  43  to  14,  which  is  good  agreement. 
Matings  of  an  agouti  with  a  non-agouti  animal  produced  a  considerable 
excess  of  agoutis,  viz,  58  agouti  to  42  non-agouti,  where  50  to  50  is  the 
expected  distribution.  The  departure  from  the  expected  equality  of 
agouti  and  non-agouti  young  is,  however,  not  probably  significant. 


TABLE  20.  —  Classification  of  the  F2  young  of  &1002,  obtained  from 
classified  in  table  19. 


animals 


Nature  of  FI  mating. 

Dark-eyed 
intense. 

Dark-eyed 
dilute. 

Red-eyed. 

Golden 
agouti. 

Black. 

Yellow 
agouti. 

Sepia. 

Silver 
agouti. 

Sepia. 

Golden  agouti  X  black  

12 
2 
4 

4 
4 

3 
2 
4 
5 
11 

1 

3 
2 
10 

1 
3 

2 
12 
28 

7 

1 
2 

6 
7 
12 

Golden  agouti  X  silver  agouti  
Black  X  silver  agouti  

Yellow  agouti  X  silver  agouti  .... 
Dark-eyed  sepia  X  silver  agouti  .  . 
Silver  agouti  X  silver  agouti  

Silver  agouti  X  sepia  (red-eyed)  .  . 
Total  

18 

8 

25 

16 

53 

28 

6 

4 

22 

15 

18 
35 

9 
19 

Red-eye  X  red-eye  

Nature  of  FI  mating. 

Pink-eyed. 

Red-and-pink- 
eyed. 

Albino. 

Agouti 

Non- 
agouti. 

Agouti. 

Non- 
agouti. 

Golden  agouti  X  black  

1 

3 

2 

2 

4 
11 
7 
11 

Golden  agouti  X  silver  agouti  .... 
Black  X  silver  agouti  

1 

Yellow  agouti  X  silver  agouti  

Dark-eyed  sepia  X  silver  agouti  .  . 
Silver  agouti  X  silver  agouti  

Silver  agouti  X  sepia  (red-eyed)  .  . 
Total  

1 

1 

5 

2 

33 

Dark-eye  X  red-eye  

1 

1 

5 

2 

15 

18 

Red-eye  X  red-eye  

If  we  summarize  the  matings  in  which  every  mother  and  father  is 
known  to  have  been  capable  of  producing  albinos,  we  have  96  colored 
to  28  albino  young;  expected  93  to  31 — a  very  good  agreement  with 
expectation. 

Summarizing  the  matings  between  a  red-eyed  male  and  a  dark-eyed 
female  known  to  have  been  capable  of  producing  red-eyevd  young,  we 
get  40  dark-eyed  and  27  red-eyed;  expected  33.5  and  33.5.  This 


GUINEA-PIGS   FROM   AREQUIPA. 


35 


apparent  deficiency  of  red-eyed  young  may  have  been  due  to  our  failure 
at  first  to  distinguish  dark-eyed  sepias  from  red-eyed  sepias,  which  look 
very  much  alike  when  first  born.  In  the  summary  all  sepias  are  treated 
as  dark-eyed  unless  a  specific  record  in  the  ledger  indicates  that  they 
were  red-eyed. 

Matings  yielding  pink-eyed  young  produced  17  non-pink-eyed  and 
6  pink-eyed  young,  which  is  good  agreement  with  the  expected  3  to  1 
ratio. 

BACK-CROSS  AND  OTHER  OFFSPRING  OF  d"  1002. 

Male  1002  was  mated  with  certain  of  his  Fx  daughters,  producing  90 
young  of  10  different  color  classes,  as  indicated  in  table  21.  He  was 
later  mated  with  certain  of  the  female  young  produced  by  the  matings 
last  described,  these  females  being  both  his  daughters  and  his  grand- 
daughters and  so  "f -blood"  Arequipa  tracing  back  to  himself.  (See 

TABLE  21. — Classification  of  young  of  &1002  by  his  F\  daughters  (table  19). 


Mothers. 

Intense  dark- 
eyed. 

Dilute  dark- 
eyed. 

Red-eyed  . 

Pink-eyed. 

Red-and- 
pink-eyed. 

Golden 
agouti. 

Black. 

Yellow 
agouti. 

Sepia. 

Silver 
agouti. 

Sepia. 

Agouti. 

Non- 
agouti. 

Agouti. 

Non- 
agouti. 

4  black  

1 

6 

3 
2 
13 

8 

3 

1 
3 

7 

11 
5 

3 

1 
7 
2 

2 

3 

2 

1 
2 

1 
2 

1 

1  sepia  (dark-eyed). 
6  silver  agouti  
3  sepia  (red-eyed)  .  . 

Total  

1 

6 

26 

14 

16 

13 

7 

3 

3 

1 

table  22.)  The  table  22  matings  have  produced  to  date  (April  1915) 
61  young,  distributed  in  9  of  the  10  classes  represented  among  the  table 
21  young.  The  classes  of  young  recorded  in  tables  21  and  22  are  the 
same  as  those  represented  among  the  F2  young  (table  20),  with  the 
exception  of  albinos,  which  are  never  produced  by  d"  1002,  since  he  does 
not  transmit  albinism,  which  is  recessive  to  both  of  its  allelomorphs. 
As  regards  the  characters  in  which  6"  1002  is  heterozygous,  there  is 
evidence  from  tables  20  to  22  that  in  the  case  of  each  he  forms  equal 
numbers  of  gametes  bearing  the  dominant  and  the  recessive  allelo- 
morphs respectively.  By  agouti  daughters  he  has  had  50  agouti  and 
15  non-agouti  young;  expected,  49  and  16.  By  non-agouti  daughters 
he  has  had  45  agouti  and  41  non-agouti  young;  expected,  43  of  each. 
Combining  these  totals  with  those  recorded  in  table  19,  we  find  that 
in  all  matings  with  non-agouti  animals  he  has  sired  101  agouti  and 
73  non-agouti  young,  a  not  improbable  chance  deviation  from  the  ex- 
pected equality  of  the  two  classes. 

By  red-eyed  daughters  cf!002  has  had  51  dark-eyed  and  40  red-eyed 
young.    Adding  to  this  result  that  recorded  in  table  19  (last  category 


36 


INHERITANCE    IN    GUINEA-PIGS. 


of  matings),  which  has  the  same  expectation  of  red-eyed  young  (50  per 
cent),  we  get  a  total  of  58  dark-eyed  and  51  red-eyed,  fairly  good 
agreement  with  the  expected  equality. 

By  dark-eyed  daughters  which  have  produced  red-eyed  young  and 
so  have  shown  that  they  transmit  either  red-eye  or  albinism,  cf  1002  has 
produced  18  dark-eyed  and  16  red-eyed  young;  expected  25.5  and  8.5. 
Doubtless  other  daughters  which  have  not  chanced  to  produce  red-eyed 
young  in  the  litters  recorded  are  also  heterozygous  for  red-eye,  in  which 
case  their  recorded  litters  should  be  added  to  the  foregoing.  If  this 
were  done,  the  observed  departure  in  this  case  from  the  expected  3  to  1 
ratio  would  doubtless  disappear. 

TABLE  22. — Classification  of  young  of  &1002  by  his  granddaughters  which  were  also   his 

daughters  (table  21). 


Mother. 

Intense  dark- 
eyed. 

Dilute  dark- 
eyed. 

Red-eyed. 

Pink-eyed. 

Red-and- 
pink-eyed. 

Golden 
agouti. 

Black. 

Yellow 
agouti. 

Sepia. 

Silver 
agouti. 

Sepia. 

Agouti. 

Non- 
agouti. 

Agouti. 

Non- 
agouti. 

2  golden  agouti  .... 
1  black  

4 

1 

1 

2 
2 
4 
4 
3 

1 

1 

1 

1 

1  yellow  agouti  .... 
3  sepia  (dark-eyed)  . 
2  silver  agouti  
2  sepia  (red-eyed)  .  . 
2  non-agouti  (pink- 
eyed)  

2 
1 
1 

1 
1 

1 

2 
1 

2 
3 

2 
4 

1 

1 
1 

3 

2 

3 

2 

1 
1 

2  agouti    (red-and- 
pink-eyed)  

Total  

4 

1 

16 

6 

10 

8 

7 

4 

5 

0 

By  pink-eyed  daughters,  d"  1002  has  produced  7  pink-eyed  young  and 
8  with  eyes  not  pink — complete  agreement  with  the  expected  equality. 
By  daughters  not  pink-eyed,  but  which  nevertheless  are  clearly  hetero- 
zygous in  pink-eye,  he  has  produced  23  pink-eyed  and  58  not-pink-eyed 
young;  expected,  20  and  61 — an  excess  of  pinks  capable  of  explanation 
on  the  same  ground  as  the  excess  of  red-eyed  young. 

By  dilute-colored  daughters  6^1002  has  produced  52  dilute-colored 
young,  but  no  intense-colored  ones,  as  expected,  since  dilution  is 
recessive  to  intensity.  By  intense-colored  daughters  heterozygous  for 
dilution  he  has  produced  10  intense  and  9  dilute  young,  equality  being 
expected. 

MISCELLANEOUS  MATINGS  OF  THE  DESCENDANTS  OF  d"  1002. 

Matings  of  the  descendants  of  d"  1002  beyond  the  F2  generation  were 
made  chiefly  with  a  view  to  test  further  the  genetic  character  of  the  new 
varieties.  Their  results  are  presented  in  tables  23  to  28  and  serve  to 
confirm  the  interpretations  already  offered. 


GUINEA-PIGS   FROM   AREQUIPA. 


37 


Matings  of  red-eyed  animals  inter  se  have  in  most  cases  produced  only 
red-eyed  or  albino  young,  but  two  matings  have  also  produced  pink- 
and-red-eyed  young,  i.  e.,  animals  which  are  pink-eyed  but  develop  no 
yellow  in  then-  fur,  in  which  last  respect  they  differ  from  ordinary 
pink-eyed  and  agree  with  ordinary  red-eyed.  (See  tables  24  and  27.) 

TABLE  23. — Young  produced  by  matings  of  red-eyed  males,  descended  from 
<?1002,  v."ith  dark-eyed  females  of  race  B. 


Nature  of  mating. 

Dark-eyed. 

Red-eyed. 

Albino. 

Golden 
agouti. 

Black. 

Silver 
agouti. 

Sepia. 

Silver  agouti  X  black  (homozygous)  .... 
Silver  agouti  X  black  (heterozygous  in 
albinism)  

1 
20 

5 

7 
6 

9 

7 

10 

Sepia  (red  -eyed)  X  black  (homozygous)  .  . 
Total  

21 

18 

9 

7 

10 

Most  of  the  red-eyed  animals,  when  bred  inter  se,  produce  albino  as 
well  as  red-eyed  young,  showing  themselves  to  be  heterozygous  for 
albinism  and  so  of  the  formula  CrCa.  This  is  not  surprising  when  we 
recall  that  all  the  Fj.  red-eyed  animals  must  by  hypothesis  be  of  this 
formula,  and  that  two-thirds  of  the  F2  red-eyed  should  be  of  the  same 
sort.  In  a  few  matings  of  red-eyed  with  red-eyed,  which  failed  to 
produce  albino  young  (table  24),  it  is  probable  that  one  or  both  parents 

TABLE  24. — Young  produced  by  matings  inter  se  of  red-eyed  descendants 
of<?1002.    (See  also  table  27). 


Nature  of  mating. 

Red-eyed 
young. 

Albino 
young. 

Silver 
agouti. 

Sepia. 

Both  parents  agouti  

56 
18 

19 
6 
9 

22 
11 

Only  one  parent  agouti  

Neither  parent  agouti  

Total  

74 

34 

33 

were  homozygous  for  red-eye.  Matings  of  red-eyed  with  albino  animals 
(table  25),  which  failed  to  produce  albinos  in  6  or  more  young,  afford 
clear  criteria  for  red-eyed  animals  free  from  albinism  and  so  of  formula 
CrCr.  Only  one  mating  of  a  red-eyed  animal  with  an  albino  has  pro- 
duced pink-eyed  young.  (See  table  27.)  The  red-eyed  parent  in  this 
case  (cf  48)  was  mated  with  4  other  albinos  (all  of  race  B)  without 
producing  pink-eyed  young,  but  only  red-eyed  (13)  and  albinos  (17). 
The  female  which  produced  pink-eyed  young  was  his  sister,  derived  like 


38 


INHERITANCE   IN   GUINEA-PIGS. 


himself  from  parents  known  to  transmit  pink-eye.  This  indicates  that 
the  character  pink-eye  in  guinea-pigs  (as  in  mice)  may  be  transmitted 
by  albinos.  The  fact  should  be  emphasized  that  the  pink-eyed  young 

TABLE  25. — Young  produced  by  red-eyed  descendants  of  <?  1002  mated  with 
albinos.      (See  also  table  27.) 


Nature  of  red-eyed  parent. 

Red-eyed 
young. 

Albino 
young. 

Silver 
agouti. 

Sepia. 

Silver  agouti,  heterozygous  for  albinism  

21 

11 
31 
11 
20 

17 
34 

Sepia,  heterozygous  for  albinism  

Silver  agouti  (homozygous  for  red-eye)  

18 

Sepia  (homozygous  for  red-eye)  

Total  

39 

73 

51 

produced  hi  this  mating  were  also  red-eyed,  i.  e.,  were  non-yellow,  for 
red-eyed  animals  may  carry  pink-eye  as  a  recessive  character,  and  con- 
versely pink-eyed  may  carry  red-eye  as  a  recessive  character.  How- 
ever, if  these  recessive  characters  crop  out  as  recessive  individuals 
from  a  mating  of  two  like  parents  with  each  other,  it  can  in  either  case 
occur  only  in  the  form  of  the  double  recessive,  both  pink-  and  red-eyed. 

TABLE  26. — Young  produced  by  pink-eyed  descendants  of  <?1002,  mated  inter  se. 


Nature  of  mating. 

Pink-eyed. 

Pink-and- 
red-eyed. 

Albino. 

Agouti. 

Non- 
agouti. 

Agouti. 

Non- 
agouti. 

Both  parents  agouti  

15 
4 

2 
4 

1 

1 
7 

One  parent  agouti,  one  non-agouti  .  .  . 
Total  

19 

6 

1 

0 

8 

Pink-eyed  animals  (with  yellow  in  their  fur)  have  made  their  appear- 
ance as  recessives  produced  by  mating  dark-eyed  animals  inter  se. 
(See  tables  20,  22,  and  27.)  In  some  cases  red-eyed  young  have  been 
produced  by  the  same  matings,  or  pink-and-red-eyed  or  albinos,  for 
pink-eye  seems  to  be  quite  independent  of  the  color  factor  in  its  inherit- 
ance. Pink-eyed  animals  mated  inter  se  have  produced  only  pink-eyed, 
pink-and-red-eyed,  and  albino  young.  (See  table  26.)  Any  of  these 
three  forms  so  derived  will  doubtless  be  found  to  transmit  pink-eye  in 
every  gamete. 

Pink-and-red-eyed  animals  of  whatever  origin  have  been  found  to 
produce  (when  mated  with  each  other)  only  pink-and-red-eyed  young 
or  albinos.  But  the  record  as  regards  albinos  is  doubtful.  Two 


GUINEA-PIGS   FROM   AREQUIPA. 


39 


albino  young  have  been  recorded  as  produced  by  c?88  mated  with  his 
daughters,  9204  and  9205;  but  this  same  male  mated  with  albino 
females  of  race  B  produced  11  red-eyed  young  but  no  albinos,  for  which 
reason  it  seems  very  doubtful  whether  he  transmits  albinism.  More 
probably  the  two  young  by  pink-and-red-eyed  mothers  were  not 
albinos,  but  very  pale-colored  non-yellow  young,  possibly  lacking  the 
extension  factor,  in  which  case  their  fur  would  be  pure  white,  then*  eyes 
being  uncolored  because  of  the  pink-eye  factor.  If  so,  they  would  be 
in  appearance  indistinguishable  from  albinos,  though  behaving  very 
differently  hi  crosses. 

TABLE  27. — Matings  of  descendants  of  &1002  which  have  produced  pink-eyed  young. 


Nature  of  mating  as  regards  — 

Dark-eyed  young. 

Red-eyed  young. 

Color  factor. 

Agouti  factor. 

Golden 
agouti. 

Black. 

Silver 
agouti. 

Sepia. 

Dark-eye  X  dark-eye  .  . 
Dark-eye  X  red-eye  .  .  . 

Agouti  X  agouti  

4 

2 

1 

8 

2 
4 
5 

.  .    .  .  Do  

Do 

Agouti  X  non-agouti  

3 

Red-eye  X  red-eye 

Agouti  X  agouti  

Red-eye  X  albino  

Non-agouti  X  non-agouti  .  . 

Total  

7 

2 

9 

11 

Nature  of  mating  as  regards  — 

Pink-eyed 
young. 

Pink-and-red- 
eyed  young. 

Albino 
young. 

Color  factor. 

Agouti  factor. 

Agouti. 

Non- 
agouti. 

Agouti. 

Non- 
agouti. 

Dark-eye  X  dark-eye. 
Dark-eye  X  red-eye  .  .  . 

Agouti  X  agouti  

1 

1 

1 
3 

2 

7 
5 

Do  

2 

1 

Do  

Agouti  X  non-agouti  
Agouti  X  agouti  

Red-eye  X  red-eye  
Red-eye  X  albino  ' 

Total  

Non-agouti  X  non-agouti  . 

3 

2 

4 

2 

12 

Nevertheless,  it  is  to  be  expected  that  pink-and-red-eyed  animals 
can  be  produced  which  are  heterozygous  for  albinism.  Such  animals 
necessarily  would  be  heterozygous  for  red-eye  also,  which  is  an  allelo- 
morph of  albinism,  and  so  would  be  of  the  formula  CrCapp,  for  it  is 
known  (1)  that  pink-eyed  animals  may  transmit  albinism;  (2)  that  red- 
eyed  animals  may  transmit  albinism;  and  (3)  that  pink-eye  and  red-eye 
are  independent  of  each  other  hi  transmission.  Consequently,  there  is 
every  reason  to  suppose  that  albinism  may  exist  as  a  recessive  allelo- 
morph of  red-eye  in  animals  which  are  both  pink-eyed  and  red-eyed. 

A  pink-eyed  animal  mated  with  a  dark-eyed  one  produced  3  dark- 
eyed  young  and  1  albino,  which  adds  to  the  evidence  that  pink-eye  is 
recessive  to  dark-eye  and  may  be  present  in  the  same  zygote  as  albin- 
ism. A  pink-eyed  animal  (9307)  mated  with  a  pink-and-red-eyed 


40 


INHERITANCE   IN   GUINEA-PIGS. 


male  (d"140)  produced  2  pink-and-red-eyed  young.  A  pink-and-red- 
eyed  male  mated  with  2  dark-eyed  females  of  race  B,  which  were  hetero- 
zygous in  albinism,  produced  4  dark-eyed  and  4  red-eyed  young. 
Another  pink-and-red-eyed  male  (140)  mated  with  a  dark-eyed  female 
descended  from  cf  1002  produced  1  pink-eyed  young,  in  which  red-eye 
was  undoubtedly  recessive.  Most  of  the  foregoing  matings  are  tabu- 
lated in  table  28. 

TABLE  28. — Character  of  young  produced  in  matings  of  pink-and-red-eyed  descendants  of  <?  1002. 


Character  of  mate. 

Character  of  mating  as 
regards  agouti. 

Dark-eyed  young. 

Red-eyed  young. 

Golden 
agouti. 

Black. 

Silver 
agouti. 

Sepia. 

Dark-eyed  

Agouti  X  agouti  

2 

2 
4 
5 

8 

2 
2 
10 

f 

Do  

Agouti  X  non-agouti  

2 

Red-eyed  

Agouti  X  agouti       

Do  

Agouti  X  non-agouti  

Pink-eyed  

Do.  

Albino  

Do  

Pink-and-red-eyed  .... 
Do  

Agouti  X  agouti  

Agouti  X  non-agouti  

Do  

Non-agouti  X  non-agouti  .  .  . 

Total 

2 

2 

19 

21 

Character  of  mate. 

Character  of  mating  as 
regards  agouti. 

Pink-eyed 
young. 

Pink-and-red- 
eyed  young. 

Albino 
young. 

Agouti. 

Non- 
agouti. 

Agouti 

Non- 
agouti. 

Dark-eyed  

A 
A 
A 
A 

gouti  X  agouti  

1 

4 

1 

1 
15 

3 
1 

2 
18 
6 

2'(?) 

1 

2(?) 

Do  

gouti  X  non-agouti  
gouti  X  agouti 

Red-eyed  . 

Do  

gouti  X  non-agouti  .... 
.  .  Do-   . 

Pink-eyed  

Albino  

Do"  

Pink-and-red-eyed  .  . 
Do  

A 

A 

N 

gouti  X  agouti  

gouti  X  non-agouti  

Do  

on-agouti  X  non-agouti  . 

Total 

1 

0 

21 

30 

1  +4  (?) 

Pink-and-red-eyed  males  mated  with  albinos  of  races  free  from  pink- 
eye produce  red-eyed  or  albino  young,  but  not  pink-eyed  young,  since 
pink-eye  also  is  a  recessive  character  and  becomes  visible  only  when 
doubly  represented  in  the  zygote. 

It  is  clear,  accordingly,  that  when  pink-and-red-eyed  animals  are 
mated  with  red-eyed  animals  (or  albinos),  young  are  produced  which 
are  red-eyed,  but  in  which  pink-eye  is  recessive;  and  when  the  same 
pink-and-red-eyed  animals  are  mated  with  pink-eyed  animals,  young 
are  produced  which  are  pink-eyed,  but  in  which  red-ey^  is  recessive. 
Hence  the  two  characters,  pink-eye  and  red-eye,  are  independent  of  each 
other,  though  red-eye  is  the  dominant  allelomorph  of  albinism,  with 
which  pink-eye  is  wholly  unrelated. 


GUINEA-PIGS   FROM   AREQUIPA.  41 

SUMMARY  ON  THE  AREQUIPA  DOMESTICATED  RACE. 

1.  A  domesticated  male  guinea-pig  obtained  from  the  cabin  of  a 
native  in  Arequipa,  Peru,  has  proved  to  be  of  great  interest  because  of 
the  large  number  of  color  mutations  which  it  either  possesses  or  trans- 
mits without  itself  manifesting  them.    Two  wholly  new  variations 
(red-eye  and  pink-eye)  were  obtained  from  this  animal  as  recessive 
characters.    The  former  has  been  obtained  subsequently  from  the  lea 
race  and  the  latter  from  a  race  of  guinea-pigs  brought  from  Lima  by 
Professor  Brues.    Both   are  probably  variations  of  long  standing 
among  the  guinea-pigs  kept  by  the  natives  in  Peru,  but  seem  not  previ- 
ously to  have  been  observed  among  guinea-pigs  in  Europe  or  North 
America. 

2.  Red-eye  is  a  Mendelian  allelomorph  of  albinism,  of  dilute  pig- 
mentation, and  of  intense  pigmentation,  the  four  being  quadruple  alle- 
lomorphs (Wright,  1915).    A  gamete  may  transmit  one  of  the  four, 
but  not  more;  a  zygote  may  contain  and  transmit  (separately)  two  of 
the  four,  but  not  more.     Dominance  is  in  the  order  of  decreasing 
intensity,  viz,  (1)  intensity,  (2)  dilution,  (3)  red-eye,  (4)  albinism. 
Intensity  and  dilution  affect  all  pigments  similarly;  red-eye  and  albin- 
ism inhibit  yellow  completely,  but  affect  black  in  very  different  de- 
grees, the  inhibition  of  black  being  nearly  complete  in  albinism,  but 
being  partial  only  in  red-eye.    Red-eye  is  a  variation  unknown  as  yet 
in  any  other  animal,  but  the  sooty  coat  of  young  Himalayan  rabbits 
possibly  is  a  parallel  variation,  and  the  same  may  be  true  of  Siamese  cats. 

3.  Pink-eye  is  a  variation  wholly  independent  genetically  of  albinism. 
It  affects  only  black  (or  brown)  pigments,  the  intensity  of  yellow  pig- 
ment being  unimpaired  in  its  presence.    A  similar  variation  (genetically 
and  physiologically)  occurs  in  mice  and  also  in  rats. 

4.  The  new  variations  (red-eye  and  pink-eye)  have  formed,  with  the 
previously  known  unit-character  variations  of  guinea-pigs,  many  new 
unit-character  combinations,  which  are  here  described. 

5.  From  the  crosses  of  the  Arequipa  domesticated  guinea-pig  with 
other  guinea-pigs,  involving  a  maximum  number  of  color  factors,  no 
evidence  is  forthcoming  that  any  two  of  the  factors  are  "coupled"  or 
"linked." 


42  INHERITANCE   IN   GUINEA-PIGS. 

SIZE  INHERITANCE  IN  GUINEA-PIG  CROSSES. 
PREVIOUS  WORK  ON  SIZE  INHERITANCE. 

For  several  years  my  pupils  and  I  have  been  engaged  in  studying  the 
inheritance  of  size  among  tame  or  domesticated  animals,  a  subject 
deserving  of  careful  investigation  both  because  of  its  economic  impor- 
tance and  because  of  the  light  which  it  may  throw  on  general  theories 
of  heredity.  A  preliminary  study  based  on  skeletal  measurements  of 
rabbits  was  published  in  1909  (Castle  et  aL),  which  seemed  to  show  that 
size  inheritance  is  "blending"  and  does  not  involve  the  segregation  and 
recombination  of  distinct  Mendelian  size-factors.  MacDowell  (1914), 
at  my  suggestion,  repeated  this  work  on  a  larger  scale  and  with  similar 
observational  results,  establishing,  however,  the  additional  fact  that 
an  F2,  or  a  back-cross  generation,  usually  shows  greater  variability  in 
size  than  an  Fx  generation,  following  a  cross  between  animals  of  unlike 
sizes,  though  the  general  result  in  both  cases  is  the  production  of  inter- 
mediates. On  theoretical  grounds  MacDowell  favored  the  Nilsson- 
Ehle  view  that  all  variation,  even  when  continuous,  is  caused  by  genetic 
factors  themselves  discontinuous,  and  that  blending  inheritance  in- 
volves multiple  segregating  factors.  But  MacDowell  points  out  that 
this  interpretation  is  not  the  only  one  of  which  his  observations  are 
capable.  The  genetic  purity  of  his  material  also,  while  sufficient  to 
establish  the  general  blending  character  of  the  inheritance,  is  not  suffi- 
cient to  meet  the  extreme  demands  of  the  multiple-factor  hypothesis. 

At  the  same  time  that  MacDowell  was  making  his  observations  on 
size  inheritance  in  rabbits,  Detlefsen  (also  in  my  laboratory)  made 
observations  on  size  inheritance  in  crosses  between  Cavia  rufescens  and 
the  guinea-pig.  He  was  unable  to  rear  an  F2  generation,  because  of 
the  complete  sterility  of  the  male  hybrids,  but  from  a  study  of  repeated 
back-crosses  concluded  that  "there  were  no  great  differences  in  vari- 
ability in  the  back-crosses  of  hybrids  to  guinea-pigs  which  would  indi- 
cate segregation  and  recombination  of  factors  for  size."  This  conclu- 
sion he  reached  without  theoretical  bias,  for  he  adds:  "The  results  in 
no  way  controvert  the  possibility  that  size  may  be  due  to  factors  which 
are  inherited  in  Mendelian  fashion;  but  segregation  was  not  apparent 
in  these  classes  of  matings  in  this  species  cross." 

My  colleague,  Dr.  John  C.  Phillips,  at  about  the  same  time  (1912, 
1914),  undertook  crosses  of  very  pure  races  of  ducks,  which  differed 
widely  in  size,  viz,  Rouens  and  Mallards.  The  two  parent  races  did 
not  overlap  in  variability  in  size.  The  F!  offspring  were  of  intermediate 
weight,  as  were  also  the  F2  offspring.  The  F2  generation  of  63  indi- 
viduals included  only  1  individual  which  fell  outside  the  range  of  the 
70  F!  individuals,  though  the  standard  deviation  of  the  ]^2  generation 
was  somewhat  larger  than  that  of  the  F!  generation.  Four  body- 


SIZE.  43 

dimensions  of  the  Fx  and  F2  ducks  were  also  studied  by  Phillips,  viz, 
length  of  bill,  tarsus,  neck,  and  total  length.  Length  of  bill  and  length 
of  neck  were  slightly  more  variable  in  F2  than  in  F^  length  of  tarsus 
was  slightly  less  variable  in  F2  than  in  Fj,  while  total  length  was  more 
variable  in  males  but  less  variable  in  females  hi  F2  than  in  F!.  It  thus 
appears  that  F2  is  not  even  uniformly  more  variable  than  F!  in  size  char- 
acters in  this  the  purest  material  that  had  thus  far  been  investigated  as 
to  size  inheritance  among  animals.  Yet  this  supposed  increase  of  vari- 
ability is  the  only  criterion  of  segregation  in  size  crosses  which  has  been 
discovered  or  even  suggested.  Surely  this  is  a  wholly  inadequate  basis 
on  which  to  rest  a  theory  that  all  inheritance  is  based  on  discontinuous 
Mendelian  factors. 

While  the  several  investigations  of  size  inheritance  in  rabbits,  guinea- 
pigs,  and  ducks  were  in  progress,  but  before  their  outcome  had  become 
apparent,  the  Peruvian  expedition  brought  to  the  laboratory  material 
which  seemed  very  favorable  for  such  studies,  and  I  have  constantly 
kept  in  mind  its  use  in  this  way.  Cavia  cutleri  from  Peru  gave  us  a 
small  race  of  undoubted  purity,  less  than  half  the  size  of  the  guinea-pig, 
but  which  has  been  found  to  produce  fertile  hybrids  with  it,  which  per- 
mits obtaining  an  F2  generation,  a  thing  impossible  with  the  rufescens 
hybrids.  The  lea  race  and  the  Arequipa  race  have  also  afforded  valu- 
able material  for  size  crosses  with  our  own  long-inbred  and  standardized 
races  of  guinea-pigs. 

The  results  which  have  been  obtained,  so  far  as  the  demonstration 
of  mendelizing  size-factors  is  concerned,  are  negative,  like  those  previ- 
ously obtained,  though  in  some  respects  the  material  is  more  satis- 
factory. But  from  their  bearing  on  the  question  whether  or  not  size 
inheritance  depends  upon  discontinuous  Mendelian  factors,  these  ob- 
servations have,  it  is  believed,  several  interesting  features  which  will 
become  apparent  as  the  description  progresses. 

WEIGHTS  AND  GROWTH  CURVES  OF  CAVIA  CUTLERI,  OF  VARIOUS 
GUINEA-PIG  RACES,  AND  OF  THEIR  HYBRIDS. 

It  will  be  recalled,  from  the  description  of  the  color  inheritance 
crosses,  that  cutleri  males  were  crossed  with  females  of  two  inbred  races 
of  guinea-pigs,  which  we  have  designated  races  B  and  C  respectively. 
Many  observations  have  been  made  on  the  weight  of  race  B  covering 
the  period  from  birth  to  old  age.  These  afford  an  accurate  knowledge 
of  the  variability  in  weight  of  race  B,  and  of  the  normal  growth  rate  of 
animals  of  this  race.  Our  knowledge  of  the  weight  of  race  C  is  less 
complete,  though  this  race  is  equally  inbred  and  appears  not  to  be  more 
variable  in  size  than  race  B.  Its  average  size  is  probably  a  little  greater 
than  that  of  race  B,  but  the  difference  is  negligible  in  comparison  with 
the  difference  of  both  from  the  size  of  C.  cutleri.  In  the  hybridization 
experiments,  race  C  hybrids  were  bred  inter  se,  as  were  also  the  race 


44 


INHERITANCE   IN   GUINEA-PIGS. 


B  hybrids,  and  in  no  case  were  hybrids  from  the  two  races  bred  with 
each  other.  Nevertheless,  the  results  obtained  in  the  two  cases  were  so 
similar  that  for  statistical  purposes  it  was  thought  best  to  combine 
them.  Race  B  is  taken  as  the  standard  guinea-pig  race  with  which  the 
hybrids  are  compared. 

For  a  period  of  about  a  year  and  a  half  all  cutleri  individuals  in  the 
laboratory,  whether  of  pure  race  or  hybrids,  were  weighed  two  or  three 
times  a  month.  In  this  way  records  were  obtained  from  which  growth 
curves,  averages  of  weight,  etc.,  can  be  deduced.  The  repeated  and 
frequent  weighings  allow  the  detection  of  periods  of  depression  due  to 
illness  or  poor  feeding.  Due  allowance  has  been  made  for  all  such 
observations,  as  well  as  for  increase  in  weight  of  females  through 
pregnancy.  Nevertheless,  observations  on  weight  are  at  best  not 


cf  RaceS. 


200 


Age  in  Days  40 


FIG.  1. — Growth-curves  of  C.  cutleri  and  of  race  B  guinea-pigs,  the  growth-curve  of 
each  sex  being  shown  separately. 

altogether  satisfactory,  since  they  are  subject  to  fluctuation  through 
conditions  of  food,  accumulations  of  fat  when  maturity  has  been 
reached,  etc.  Greater  value  attaches  to  the  bone  measurements  of 
fully  adult  individuals  (over  1  year  old)  so  far  as  individual  varia- 
bility is  concerned.  But  the  observations  on  weight  afford  a  basis 
entirely  satisfactory  for  the  determination  of  average  sizes  and  average 
growth  curves  in  different  classes  of  hybrids.  Incidentally  they  afford 
a  control  on  the  bone  measurements,  for  they  indicate  cases  of  abnormal 
growth  (through  disease,  fighting,  or  other  cause)  and  allow  of  either 
remedying  conditions  or  rejecting  suspicious  material. 

Pure  cutleri  young  of  both  sexes  are  of  about  the  same  average  weight 
at  birth,  viz,  50  grams  (see  fig.  1).  The  females  at  first  grow  a  little 
faster  than  the  males,  a  fact  perhaps  correlated  with  their  earlier  sexual 
maturity.  At  about  50  days  of  age  the  two  sexes  are  of  practically  the 
same  weight,  the  males  having  again  caught  up  with  the  females,  and 


SIZE. 


45 


subsequently  the  males  are  heavier.  The  average  adult  weight  of  a 
female  is  about  400  grams,  that  of  a  male  about  420  grams. 

Race  B  animals  of  both  sexes  weigh  on  the  average  about  80  grams  at 
birth  (see  fig.  1),  but  females  grow  at  first  a  little  faster  than  males, 
so  that  between  10  and  50  days  of  age  females  are  slightly  heavier. 
But  the  males  soon  catch  up  with  the  females  and  from  50  days  on  are 
heavier.  The  same  difference  between  the  growth  curves  of  the  two 
sexes  is  observable  here,  as  in  Cavia  cutleri.  The  phenomenon  is  pos- 
sibly a  general  one  among  mammals.  Earlier  maturity  of  the  female 
is  attended  by  more  rapid  growth,  but  the  ultimate  weight  attained  by 
males  is  greater.  There  is  no  indication  in  our  observations  that  the 
attainment  of  sexual  maturity  is  followed  by  any  slowing-up  of  the 
growth  rate  in  either  sex. 

In  the  growth  of  both  C.  cutleri  and  of  race  B,  as  in  other  growth- 
curves  to  be  described,  the  curve  is  at  first  concave  upward,  but  later 
becomes  convex  upward.  This  agrees  with  observations  on  rabbits, 
fowls,  and  other  organisms,  and  its  significance  has  been  discussed 
elsewhere  (Castle  et  al.,  1909). 


Age  in  Days  40 
Fia.  2 — Growth  curves  of  race  B  and  cutleri  males  and  of  their  male  hybrids,  both  FI  and  F2. 

F!  hybrid  males  (from  the  cross  cf  cutleri  X  9  race  B  or  C,  fig.  2) 
weigh  about  85  grams  at  birth,  i.  e.,  they  are  slightly  heavier  than  the 
young  of  either  pure  race,  a  lead  which  they  retain  throughout  subse- 
quent life.  At  maturity  they  weigh  about  890  grams,  as  compared 
with  800  grams,  the  average  adult  weight  of  race  B  males,  and  420 
grams,  the  average  adult  weight  of  pure  cutleri  males.  The  females 
(fig.  3)  weigh  about  the  same  as  the  males  at  birth,  or  are  even  a  little 
heavier,  but  soon  begin  to  grow  less  rapidly,  weighing  about  750  grams 
when  1  year  old.  The  F2  hybrids  of  both  sexes  are  smaller  than  the 
F!  hybrids  from  birth  on,  a  fact  of  undoubted  significance.  (See  figs. 
2  and  3.)  The  superior  growth  impetus  which  was  produced  by 


46 


INHERITANCE   IN   GUINEA-PIGS. 


hybridization  has  not  been  retained  in  the  second-generation  offspring, 
which  sink  as  regards  weight  to  a  position  intermediate  between  the 
parent  races.  Nevertheless  the  F2  hybrids  are  nearer  to  race  B  than 
to  cutleri  in  adult  size,  which  fact  suggests  that  not  all  the  growth 
impetus  furnished  by  hybridization  has  yet  been  dissipated.  In  form 
of  growth  curve  the  F2  hybrids  are  also  intermediate.  The  growth 
curve  at  first  rises  rapidly,  due  in  part  perhaps  to  the  good  milk-giving 
qualities  of  then*  vigorous  F!  hybrid  mothers,  but  in  part  probably  to 
inheritance  of  cutleri  qualities,  since  the  cutleri  growth  curve  is  a  rela- 
tively steep  but  low  one,  indicating  rapid  growth  at  first  and  early 
maturity.  The  F2  hybrids  also  grow  rapidly  at  first,  being  consider- 
ably heavier  than  race  B  animals  until  an  age  of  120  to  150  days  has 
been  reached.  Then  they  fall  below  and  stay  below  the  weight  of 
race  B  animals,  running  a  course  nearly  parallel  with  that  of  pure 
cutleri  animals,  whereas  the  growth  curve  of  the  F!  animals  more  nearly 
approached  that  of  race  B  animals. 


FIG.  3. — Growth  curves  of  race  B  and  cutleri  females  and  of  their  female  hybrids,  both  F!  and  Fj. 

While  we  are  on  this  subject  it  may  be  well  to  refer  to  the  growth 
curves  observed  in  the  cross  between  the  Arequipa  male,  1002,  and 
females  of  race  B  (or  of  similar  character).  (See  fig.  4.)  The  data  for 
the  growth  curves  of  males  are  more  complete  in  this  case  than  the 
data  for  females  and  accordingly  only  the  former  will  be  considered. 
The  F!  animals  are  of  great  size  and  vigor,  attaining  an  average  adult 
weight  of  over  1,200  grams.  The  F2  animals  are  even  larger  at  birth 
than  the  F1  animals,  a  fact  which  indicates  that  the  size  of  the  mother 
has  something  to  do,  other  than  through  heredity,  with  the  size  of  the 
young  at  birth,  for  the  F2  young  rapidly  lose  the  lead  which  they  had 
in  weight  at  birth  over  their  F!  parents,  and  subsequent  to  40  days  of 
age  fall  below  them  in  weight.  At  maturity  they  weigh  less  than  1,000 
grams,  having  lost  more  than  half  of  the  gain  which  the  F!  animals 
showed  over  race  B  animals.  This  difference,  it  should  be  stated 
emphatically,  is  not  due  to  environmental  conditions  of  any  sort,  such 


SIZE. 


47 


as  season  of  the  year,  food,  or  the  like,  for  it  exists  between  lots  of  F! 
and  F2  animals  reared  simultaneously  and  treated  exactly  alike.  It  is 
clear,  therefore,  that  a  cross  of  distinct  races,  whether  wild  or  domesti- 
cated, brings  a  stimulus  to  growth  which  leads  to  the  attainment  of 
size  considerably  beyond  that  which  truly  inherited  size  factors  would 
produce.  This  stimulus,  however,  lasts  unimpaired  for  only  a  single 
generation.  But  if  it  lasts  at  all  into  a  second  generation,  and  if  its 
persistence  is  not  uniform  in  amount  in  all  cases,  it  is  evident  that  it 
would  increase  the  variability  of  F2  as  compared  with  Fle  This  is  a 
matter  requiring  careful  consideration  when  the  significance  of  increased 
variability  in  F2  is  considered. 


AgdnDays    40 


FIG.  4. — Growth  curves  of  race  B  males  and  of  the  male  hybrids,  both  FI  and  Fz,  between  the 
Arequipa  male  1002  and  females  of  race  B  or  similar  races. 

SKELETAL  MEASUREMENTS  OF  CAVIA  CUTLERI,  OF  VARIOUS  RACES 
OF  GUINEA-PIGS,  AND  OF  THEIR  HYBRIDS. 

It  has  been  stated  that  skeletal  measurements  of  adult  animals  are 
considered  more  reliable  criteria  of  size  than  total  body-weight.  For 
this  reason  we  have  carefully  preserved  for  study  the  skull  and  the 
long  bones  of  the  right  fore  leg  and  right  hind  leg  of  each  adult  animal 
which  died  a  natural  death  or  was  killed,  in  the  races  whose  size  was 
under  investigation.  Observations  made  by  MacDowell,  Detlefsen, 
Wright,  and  Fish  (see  MacDowell,  1914,  appendix)  have  shown  the  vari- 
ous long  bones  of  the  legs  to  be  closely  correlated  in  length,  so  that  it 
seems  sufficient  for  our  purpose  to  measure  a  single  one  of  these,  and 
we  have  chosen  for  this  purpose  the  femur.  On  this  we  have  taken  the 


48  INHERITANCE   IN   GUINEA-PIGS. 

length  measurement  as  indicated  on  MacDowell's  figure  5,  F.  Two 
observations  have  also  been  made  of  skull  dimensions,  one  of  basilar 
skull  length  as  indicated  in  MacDowell's  figure  1,  0.  M.,  and  the  other 
of  maximum  zygomatic  width  (Z).  The  measurements  here  dealt  with 
are  found  upon  repeated  measurement  to  be  accurate  within  0.1  mm. 
The  observations  are  combined  in  classes  of  5  mm.  range  in  tables  29 
to  31  for  the  several  races  and  hybrids  studied.  We  may  consider 
first  the  observations  on  skull  length. 

THE  CUTLERI  HYBRIDS. 

Ten  adult  cutlcri  females  have  skull  lengths  distributed  as  shown  in 
table  29.  The  range  extends  over  10  classes;  the  mean  is  51.55  mm., 
and  the  standard  deviation  13.50  mm.  Twenty-eight  adult  females  of 
race  B  have  a  range  in  skull  length  of  15  classes;  their  mean  is  58.14 
mm.,  and  the  standard  deviation  19.75  mm.  F!  hybrid  females 
between  cuileri  males  and  females  of  races  B  and  C  available  for  study 
number  24,  with  a  range  of  13  classes,  a  mean  skull  length  of  57.70  mm., 
and  a  standard  deviation  of  16.85  mm.  These  figures  indicate  (like 
the  weight  observations)  that  the  Fl  hybrids  are  practically  as  large 
as  the  larger  parent  race  and  not  more  variable.  The  33  F2  hybrids 
studied  show  a  range  of  18  classes,  with  a  mean  at  54.35  mm.  and  a 
standard  deviation  of  17.20  mm.  The  F!  mean  was  about  3  mm. 
greater  than  the  intermediate  between  the  races  crossed,  but  the  F2 
mean  practically  coincides  with  it.  Judged  by  the  standard  deviation, 
F2  is  not  more  variable  than  pure  race  B  and  is  only  slightly  more 
variable  than  F!.  The  means  show  in  Fx  an  increase  in  size  over  that 
we  should  expect  through  inheritance,  but  a  loss  of  this  increase  in  F2. 

Observations  on  the  male  hybrids  from  the  same  cross  are  recorded 
in  the  next  four  rows  of  table  29.  The  mean  of  the  F!  hybrids  is 
again  greater  than  that  of  either  pure  race  and  surpasses  the  inter- 
mediate point  by  nearly  4.5  mm.  The  mean  of  the  F2  hybrids  is  close 
to  the  intermediate,  which  it  exceeds  by  about  0.6  mm.  The  vari- 
ability (standard  deviation)  of  F2,  however,  is  considerably  greater  than 
that  of  F!  and  even  exceeds  that  of  pure  race  B.  Particularly  note- 
worthy is  the  occurrence  of  one  very  large  F2  individual,  nearly  as  large 
as  the  largest  F!  individual.  Compare  this  with  the  occurrence  of  a 
single  very  small  F2  female,  as  small  as  the  smallest  pure  cuileri  female. 

The  cutleri  hybrids  with  races  B  and  C  show  similar  results  in  regard 
to  the  other  measurements  studied — zygomatic  width  and  femur  length. 
(See  tables  30  and  31  and  plate  6.)  In  every  case  F!  exceeds  the  means  of 
both  parent  races,  but  F2  approximates  the  intermediate  between  them, 
which  it  exceeds  by  a  fraction  of  a  millimeter  only.  In  no  case  is  the 
F2  mean  as  great  as  the  race  B  mean — that  of  the  larger  parent  race. 
These  facts,  like  the  weight  curves,  indicate  (1)  that,  so  far  as  heredity 
is  concerned,  an  exact  intermediate  between  the  parent  races  would 


SIZE. 


49 


TABLE  29.—  A  tabulation  of  skull  length  measurements  of  Cavia  cutkri  and  of  certain  races  of  guinea-pigs  and  of  their  hybrids. 

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0    0 

03 

50 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  30.—  A  tabulation  of  skull  width  measurements  of  Cavia  cutleri  and  of  certain  races  of  guinea-pigs  and  of  their  hybrids. 

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SIZE. 


51 


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52  INHERITANCE    IN   GUINEA-PIGS. 

result  from  the  cross,  but  (2)  that  a  physiological  growth  stimulus  (not 
hereditary)  results  in  F:  from  the  fact  that  the  zygotes  produced  are 
formed  by  the  union  of  gametes  from  very  dissimilar  races,  and  (3)  that 
the  increased  F!  vigor  is  largely,  but  not  entirely,  lost  in  F2.  No  evi- 
dence is  found  that  it  persists  in  full  force  in  any  F2  zygote  (with  one 
possible  exception) ,  since  the  upper  half  of  the  range  of  the  F!  zygotes 
is  almost  completely  wanting  in  F2,  while  the  absence  of  any  appreciable 
increase  of  variability  in  F2  shows  that  any  increased  vigor  due  to  the 
cross  which  persists  into  F2  persists  also  very  generally  among  the 
zygotes  of  that  generation,  so  that  practically  all  are  changed  in  the 
same  sense  and  in  like  amount;  otherwise  increased  variability  must 
result,  irrespective  of  whether  size  inheritance  occurs  other  than  by 
complete  blending. 

HYBRIDS  OF  THE  AREQUIPA  d*  1002. 

Crosses  between  the  Arequipa  cf  1002  and  females  similar  to  those 
of  race  B,  but  averaging  a  little  larger,  have  yielded  an  extensive  and 
vigorous  race  for  the  study  of  size  inheritance.  Among  the  animals  of 
this  crossed  race  the  mortality  has  been  comparatively  small,  so  that 
good  numbers  are  available.  The  male  1002,  sole  male  ancestor  of  this 
race,  is  still  alive,  so  that  his  bone  measurements  are  not  available;  but 
a  female,  1001,  secured  in  the  same  cabin  in  Arequipa  in  1911,  lived 
until  fully  grown  and  her  bones  are  available  for  comparison.  Further, 
a  son  of  cTl002  and  9  1001  lived  until  fully  grown  and  his  bones  also 
are  available.  From  the  measurements  of  these  two  and  a  comparison 
of  the  empirical  ratio  of  female  to  male  measurements  in  the  other  races 
studied,  it  is  possible  to  arrive  at  estimates  of  the  racial  size  of  the 
Arequipa  stock  which  it  is  believed  are  fairly  reliable.  These  are  given 
in  table  32,  where  it  is  further  assumed  that  the  racial  size  of  the  animals 
mated  with  cf1 1002  was  substantially  that  of  race  B,  measurements  of 
the  latter  being  given  for  comparison.  But  whether  these  assumptions 
are  sound  or  not  does  not  affect  the  validity  of  the  observations  on  the 
F!  and  F2  hybrids  from  this  cross,  which  are  valuable  as  regards  their 
interrelations,  for  the  numbers  of  adult  individuals  are  considerable 
(43  F!  and  77  F2  animals)  and  the  mortality  among  them  is  small.  F! 
in  this  experiment  (tables  29  to  31,  rows  9-12)  regularly  exceeds 
the  assumed  mid-parental  measurement,  as  in  the  crosses  previously 
considered;  F2  is  in  all  cases  close  to  the  mid-parental,  being  slightly 
greater  in  three  cases  and  slightly  less  in  three  cases.  As  regards  the 
relative  variability  of  the  two  generations,  the  standard  deviations 
indicate  that  the  F2  females  (as  compared  with  those  of  FJ  are  con- 
siderably more  variable  in  skull  length  (though  scarcely  more  so  than 
race  B)  and  are  slightly  more  variable  in  skull  width  and  femur  length. 
The  male  F2  hybrids  differ  very  little  in  variability  from  the  Fj  hybrids, 
the  standard  deviations  being  slightly  greater  in  skull  measurements 
but  less  in  femur  length. 


SIZE. 


53 


THE  ICA  HYBRIDS. 

Crosses  with  the  lea  race  were  made  principally  by  a  male  of  race  C 
whose  measurements  are  known  and  which  slightly  exceed  the  averages 
for  race  B  males;  but  a  few  crosses  with  the  lea  race  were  also  made  with 
race  B  females  (mated  with  lea  males).  The  measurements  given  in 
table  32  for  the  mates  of  the  lea  race  are  a  mean  between  the  meas- 
urements of  races  B  and  C.  The  standard  deviation  of  the  mixed 
parents  should  of  course  exceed  that  of  race  B  alone,  which  should 
increase  the  variability  of  F-i  and  F2,  but  should  not  alter  the  relative 
variability  of  these  two,  since  the  race  B  and  race  C  hybrids  were  bred 

TABLE  32. — Statistical  constants  derived  from  tables  23  to  25. 


Races. 

No.  of 
indi- 
vid- 
uals. 

Skull-length. 

Skull-width. 

Femur-length. 

Mean. 

Standard 
deviation. 

Mean. 

Standard 
deviation. 

Mean. 

Standard 
deviation. 

9  cutleri  

10 
28 
24 
33 
7 
63 
26 
24 

51.55 
58.14 
57.70 
54.35 
52.91 
60.35 
61.20 
57.26 
61.10 
58.14 
61.92 
60.44 
63.11 
60.35 
64.40 
61.86 
57.45 
59.00 
60.20 
58.84 
58.10 
62.00 
62.20 
62.17 

13.50 
19.75 
16.85 
17.20 
9.45 
15.05 
12.15 
20.00 

30.84 
34.68 
35.24 
33.26 
31.63 
36.33 
37.79 
35.24 
39.70 
34.68 
38.37 
37.35 
41.20 
36.33 
39.40 
38.87 
36.28 
35.00 
37.13 
35.63 
38.00 
38.00 
39.26 
38.73 

9.35 
10.56 
11.60 
11.45 
6.80 
11.90 
11.70 
12.05 

38.45 
41.16 
42.63 
40.38 
38.77 
42.39 
43.57 
41.32 
45.50 
41.16 
44.07 
42.95 
46.50 
42.39 
45.16 
43.15 
42.64 
42.00 
43.49 
42.06 
42.90 
42.50 
44.63 
43.44 

12.05 
12.50 
10.35 
15.60 
8.20 
10.70 
9.80 
14.20 

9  race  B  

9  Fi,  cutleri  X  B  or  C  ... 
9  F2,  cutleri  X  B  or  C  ... 
cf  cutleri  

cf  race  B  

cf  Fi,  cutleri  X  B  or  C  ... 
cf  F2,  cutleri  X  B  or  C  ... 
9  1001  Arequipa 

9  race  B  

28 
18 
41 

63 

27 
56 
8 

19.75 
12.10 
20.65 

15.05 
15.15 
17.75 
10.00 

10.00 
11.20 
22.65 

23.55 
24.55 

10.56 
9.40 
14.05 

11.90 
11.95 
11.40 
9.80 

6.30 
8.70 
16.40 

12.10 
11.80 

12.50 
13.35 
15.30 

10.70 
10.05 
11.80 
10.75 

9.05 
10.85 
16.10 

17.60 
17.80 

9  Fi,  Arequipa  X  race  B  . 
9  F2,  Arequipa  X  race  B  . 
cf  Arequipa  (estimated)  .  . 
cf  race  B  .  .  .  

cf  FI,  Arequipa  X  race  B  . 
cf  F2,  Arequipa  X  race  B  . 
9  lea  

9  races  B  and  C  

9  Fi,  lea  X  race  B  or  C  .  .  . 
9  F2,  lea  X  race  B  or  C  .  .  . 
cf  lea  

7 
14 
10 

cf  races  B  and  C  .  . 

cf  Fi,  lea  X  race  B  or  C  .  .  . 
cf  F2,  lea  X  race  B  or  C  .  .  . 

8 
17 

entirely  distinct  from  each  other  and  are  only  tabulated  together  to 
secure  greater  numbers.  Again  in  this  cross  we  are  confronted  with  the 
same  phenomena  as  regards  the  skeletal  measurements:  (1)  in  F!  a 
substantial  increase  in  size  (least  in  skull  length  of  FI  male  hybrids) ; 

(2)  while  in  F2  a  return  is  made  toward  the  mid-parental  (mean  of  the 
races  crossed),  in  4  of  the  6  measurements  it  is  closely  approximated; 

(3)  the  standard  deviation  meanwhile  alters  little,  not  enough  to  have 
significance ;  the  lea  crosses  are  of  particular  interest  because  the  races 
mated  are  of  nearly  the  same  size.     The  phenomenon  of  increased  size 
in  F!  followed  by  a  prompt  loss  of  the  increase  in  F2  is  here  observed 


54  INHERITANCE   IN   GUINEA-PIGS. 

exactly  as  in  the  crosses  between  races  of  widely  different  and  heritably 
different  sizes,  but  without  indication  in  either  case  that  the  size  inheri- 
tance is  other  than  a  simple  and  permanent  blend. 

THEORETICAL  EXPLANATIONS  OF  SIZE  INHERITANCE  AND  OF  BLENDING 
INHERITANCE  IN  GENERAL. 

We  conclude  therefore  that,  so  far  as  present  knowledge  goes,  the 
statement  made  in  1909  that  size  inheritance  is  blending  and  does  not 
mendelize  still  holds.  This  does  not  preclude  the  possibility  that  in 
special  cases  mendelizing  factors  may  exist  which  affect  size.  For 
example,  in  man  brachydactyly  is  due  to  such  a  factor,  a  simple 
Mendelian  dominant,  as  was  first  shown  by  Farabee  (1905),  and  has 
been  confirmed  by  Drinkwater  in  the  case  of  three  separate  English 
families.  This  character  involves  a  shortening  of  the  skeleton  generally, 
but  of  the  digits  in  particular.  It  is  transmitted  only  through  affected 
individuals,  the  normal  offspring  of  affected  individuals  producing  only 
normals.  Professor  James  Wilson  has  stated  that  the  Dexter-Kerry 
cattle  of  Ireland  differ  from  ordinary  Kerry  cattle  by  a  similar  men- 
delizing  factor.  If  one  were  to  restrict  his  study  of  size  inheritance 
to  cases  such  as  these,  he  would  reach  the  conclusion  that  size  inheri- 
tance in  general  is  Mendelian,  a  wholly  mistaken  idea.  (See  Castle, 
1914.)  Such  cases  among  animals  are  distinctly  rare.  Among  culti- 
vated plants  they  seem  to  be  somewhat  commoner,  so  that  many  of  the 
inherited  size  differences  studied  by  botanists  involve  such  factors. 
One  of  the  commonest  of  these  is  involved  in  the  difference  between 
normal  (tall)  and  dwarf  habit  of  growth,  a  case  demonstrated  by 
Mendel  for  peas  in  his  original  experiments ;  but  it  is  more  than  doubtful 
whether  Mendelian  factors  produce  the  differences  in  height  observed 
among  different  races  of  tall  or  of  dwarf  peas  respectively.  The  same 
is  true  concerning  differences  in  size  or  shape  of  seeds  and  fruits,  as 
described  by  Emerson  and  Gross.  It  seems  almost  certain  that 
Mendelian  factors  are  involved  in  many  of  the  cases  studied,  but 
associated  with  other  factors  not  Mendelian,  possibly  merely  physio- 
logical, which  render  the  results  extremely  complex  and  the  variation 
seemingly  continuous  in  character.  To  have  shown  that  size  inheri- 
tance is  occasionally  affected  by  Mendelian  factors  is  not  by  any  means 
to  have  demonstrated  that  all  size  inheritance  is  due  to  Mendelian 
factors.  The  physiological  increase  of  size  due  to  the  crossing  of  unre- 
lated races  is  a  fact  of  far  greater  economic  importance  to  the  animal 
breeder  than  the  existence  of  any  Mendelian  factor  affecting  size  that 
has  thus  far  been  demonstrated. 

The  question  may  be  raised,  how  are  we  to  account  for  the  increased 
variability  of  F2  as  compared  with  F1;  if  this  is  not  due  to  segregation 
and  recombination  of  multiple  factors,  as  assumed  under  the  Nilsson- 
Ehle  principle.  (1)  This  would  be  sufficiently  accounted  for  in  the 


SIZE.  55 

case  under  discussion  by  an  unequal  persistence,  among  the  F2  zygotes, 
of  the  increased  growth  stimulus  observed  in  FI  and  due  evidently  to 
the  act  of  crossing,  not  to  inheritance.  (2)  Increased  variability  in  F2 
would  also  result  if  a  blending  occurs  in  P\,  which  is  imperfect,  so  that 
the  gametes  formed  by  the  F:  individuals  are  not  all  the  exact  mean  of 
the  parental  gametes,  but  fluctuate  around  that  mean. 

What  may  we  imagine  the  germinal  basis  of  a  blending  character  to 
be?  Perhaps  some  substance  or  ferment  which  varies  in  amount,  larger 
amounts  producing  larger  results.  If  a  5  per  cent  solution  of  cane  sugar 
were  poured  into  the  same  dish  with  a  10  per  cent  solution  and  then  sam- 
ples were  dipped  from  this  before  the  two  solutions  had  been  thoroughly 
stirred  together,  it  might  very  well  happen  that  the  samples  would  not  be 
of  uniform  strength.  Any  other  result  would  be  surprising.  A  char- 
acter genuinely  blending  in  heredity  might  be  expected  to  behave  in 
this  same  way,  the  quantitatively  different  conditions  found  in  parent 
races  not  blending  perfectly  in  a  single  generation  of  association 
together  in  an  FI  zygote,  which  therefore  would  produce  gametes  less 
uniform  in  character  than  those  of  the  respective  inbred  parent  races. 

The  multiple  factor  interpretation  of  size  inheritance,  besides  being 
superfluous,  meets  with  this  serious  logical  difficulty:  If  we  suppose 
the  difference  between  two  races  to  depend  upon  a  certain  number  of 
independent  factors  whose  action  is  cumulative,  then  a  less  difference 
must  be  due  to  fewer  factors,  and  the  fewer  factors  concerned  hi  a  cross, 
the  more  obvious  is  the  segregation.  But  we  do  not  find  it  easy  to 
detect  segregation  when  races  are  crossed  which  differ  little  in  size; 
the  general  result  is  the  same  as  when  races  are  crossed  which  differ 
widely  from  each  other.  It  is  difficult  to  detect  any  evidences  of 
segregation  unless  the  parent  races  differ  widely  from  each  other,  under 
which  condition,  if  multiple  factors  are  involved,  complete  segregation 
should  occur  least  often. 

On  the  whole,  the  hypothesis  of  quantitative  variations  in  a  blending 
character  presents  fewer  difficulties  as  an  explanation  of  size  inheritance 
than  the  hypothesis  of  multiple  unvarying  segregating  factors.  It  is 
to  be  preferred  on  the  ground  of  simplicity  alone,  but  it  also  accords 
better  with  the  results  obtained  in  other  fields.  Jennings  now  finds, 
contrary  to  his  earlier  observations  on  paramecium,  which  Calkins  and 
Gregory  were  unable  to  confirm,  that  size  is  a  character  varying  even 
in  asexual  reproduction,  within  what  would  be  a  "pure  line"  if  the 
theory  of  factorial  constancy  were  true.  My  own  observations  of 
rats  and  other  rodents  (Castle,  1915)  may  be  cited  to  show  that  even 
single  Mendelian  unit  characters  are  quantitatively  variable.  If  this 
is  so,  the  hypothesis  of  multiple  factors  as  a  general  explanation  of 
variability  is  quite  unnecessary  and  so  should  be  discarded. 


PART  II 

AN  INTENSIVE  STUDY  OF  THE  INHERITANCE  OF  COLOR 
AND  OF  OTHER  COAT  CHARACTERS  IN  GUINEA- 
PIGS,  WITH  ESPECIAL  REFERENCE  TO 
GRADED  VARIATIONS. 


BY  SEWALL  WRIGHT,  S.  D. 


COLOR  AND  ITS  INHERITANCE  IN  GUINEA-PIGS. 

The  experiments  described  in  the  following  paper  were  carried  on 
at  the  Bussey  Institution  of  Harvard  University,  between  September 
1912  and  August  1915,  under  the  direction  of  Professor  W.  E.  Castle. 
A  large  number  of  stocks  of  guinea-pigs  and  wild  cavies,  containing  an 
extensive  assortment  of  variations,  were  available  throughout  the 
experiments,  and  furnished  excellent  material  for  studies  on  inheritance. 
The  writer  wishes  here  to  express  his  gratitude  for  the  privilege  of  using 
freely  this  material  and  for  the  constant  encouragement  and  assistance 
which  Professor  Castle  has  given. 

SKIN,  FUR,  AND  EYE  COLORS  OF  GUINEA-PIGS. 

COLOR  OF  CAVIA  CUTLERI. 

The  fur  color  of  Cavia  cutleri,  the  probable  ancestor  of  the  guinea-pig, 
is  of  the  agouti  type  found  hi  most  wild  rodents,  as  well  as  in  many  other 
wild  mammals.  (See  plate  3.)  The  back  and  sides  are  slaty  black,  ticked 
with  yellow  (more  accurately,  cinnamon  buff).  An  isolated  hair  is  of 
a  dull  slate  color  at  the  base,  becoming  blacker  toward  the  tip.  Near 
the  tip  there  is  a  yellow  band  some  2  or  3  mm.  long.  The  extreme  tip 
for  1  to  2  mm.  is  black.  The  belly  is  cream-colored  (more  accurately 
cartridge  buff)  and  is  sharply  separated  from  the  ticked  sides.  An 
isolated  hair  is  pale  neutral  gray  throughout  its  basal  half  and  cream- 
colored  in  the  remaining  portion.  Cavia  rufescens  of  Brazil  has  a 
similar  ticked  coat,  but  differs  hi  showing  less  ticking  on  the  back  and 
sides  and  often  in  having  a  ticked  belly  not  sharply  separated  from  the 
sides.  The  general  appearance  is  darker.  Tame  guinea-pigs  show  a 
great  variety  of  colors  and  color  patterns  and  also  deviations  from  the 
dark  skin  and  black  eye  color  of  the  wild  species. 

MELANIN  PIGMENT. 

The  coat  colors  of  mammals  are  largely  due  to  granular  pigments  of 
a  kind  known  chemically  as  melanin.  The  pigment  in  the  hair  is 
found  principally  in  the  walls  of  air-spaces  in  the  medulla,  but  to  some 
extent  in  the  cortex,  as  described  by  Bateson  (1903)  in  mice.  Melanin 
pigments  are  also  found  in  the  skin  (principally  in  the  epidermis)  and 
in  the  iris  and  retina  of  the  eye.  A  deficiency  of  pigment  hi  the  retina 
is  revealed  by  a  red  reflection  through  the  pupil. 

PRIMARY  CLASSIFICATION  OF  FUR  COLORS. 

Three  qualitatively  distinct  melanin  pigments  are  generally  recog- 
nized in  mammals,  viz,  black,  brown,  and  yellow  (Bateson,  1903) .  There 
are  reasons,  however,  for  regarding  black  and  brown  as  more  closely 
related  to  each  other  than  either  is  to  yellow.  Black  and  brown 
granules  are  acted  upon  similarly  by  most  hereditary  factors  which  act 

59 


60  INHERITANCE   IN   GUINEA-PIGS. 

on  either.  Yellow  pigment,  on  the  other  hand,  is  acted  upon  very  dif- 
ferently from  black  and  brown  by  many  factors.  Accordingly  it  will 
be  convenient  to  use  a  term  to  include  both  black  and  brown  pigments, 
as  dark  pigments.  The  fur  colors  fall  naturally  into  two  groups,  the 
dark  and  yellow  colors,  characterized  by  the  predominant  presence  of 
dark  and  yellow  pigments  respectively. 

YELLOW  GROUP  OF  COLORS. 

In  the  yellow  group  of  colors  the  one  of  highest  intensity  is  a  rich 
yellow-orange,  which  matches  quite  well  with  ochraceous  tawny  in 
Ridgway's  color  charts  (1912).  There  are  all  gradations  from  this 
ochraceous  tawny  through  cinnamon  buff  and  cartridge  buff  to  white. 
In  this  paper  it  will  be  more  convenient  to  use  the  conventional  names, 
red,  yellow,  and  cream,  for  these  grades.  In  grading  the  guinea-pigs, 
three  samples  of  hair  have  been  used  as  standards  of  grades  called 
red0,  yellow3,  and  creamg,  respectively.  White  is  considered  to  be 
cream8.  All  of  the  yellow  colors  in  guinea-pigs  fall  into  this  series,  as 
far  as  known.  In  mice,  however,  Little  (1911)  has  shown  that  two 
dilution  series  between  red  and  white  can  be  distinguished.  There  is 
a  series  from  red  to  cream  resembling  in  appearance  (though  not  geneti- 
cally) the  guinea-pig  series.  Another  series  (the  "  dilute"  reds,  yellows, 
and  creams)  has  a  peculiar  streaky  appearance.  The  physical  relation 
between  these  two  series  is  probably  similar  to  that  between  the  sepia 
and  blue  types  of  dilution  among  the  dark  colors,  which  is  discussed 
below. 

DARK  GROUP  OF  COLORS. 

Among  the  dark  colors  there  are  at  least  three  distinct  series : 

(1)  There  is  the  series  of  neutral  grays,  passing  from  black  to  white. 
Such  colors  are  shown  by  the  blue  rabbits,  blue  mice,  and  maltese  cats. 
There  are  no  tame  guinea-pigs  known  whose  colors  fall  distinctly  into 
this  series ;  but  the  dull  black  of  the  wild  Cavia  cutleri,  especially  on  the 
belly,  is  a  neutral  gray  quite  free  from  any  brown.     Examination  of 
the  hair  of  the  blue  rabbit  under  the  microscope  shows  dense  black 
pigment  masses  alternating  with  colorless  spaces,  a  condition  described 
by  Miss  Sollas  (1909)  in  the  hair  of  the  blue  mouse  and  apparently 
comparable  to  the  clumped  condition  of  the  black  pigment  in  the 
feathers  of  blue  pigeons,  described  by  Cole  (1914). 

(2)  There  is  a  series  of  grades  from  black  through  dull  brown  and 
tow-color  to  white.     This  series  is  shown  by  dilute  black  guinea-pigs. 
The  various  shades  of  human  hair,  from  black  through  brown  to  tow- 
color,  match  samples  from  this  guinea-pig  series  very  closely.     The 
increase  in  quantity  of  pigment  in  this  series  in  passing  up  from  the 
lower  grades  is  accompanied  by  a  change  in  quality.     Yellowish-brown 
pigment  gives  way  to  black.     Dilution  of  this  sort  is  produced  inde- 


COLOR.  61 

pendently  by  different  factors,  the  combination  of  which  gives  doubly 
dilute  colors,  which  may  still  be  classed  in  the  same  series.  Dilute 
guinea-pigs  of  this  series  have  been  called  blue  in  the  literature,  but 
the  name  is  as  inappropriate  as  it  would  be  applied  to  human  brown 
hair,  and,  moreover,  tends  to  confusion  with  the  very  distinct  type 
of  dilution  of  the  blue  rabbit.  In  this  paper  the  colors  of  this  series 
will  be  called  sepia.  Grades  of  dilution  have  been  represented  by 
numbers,  as  in  the  yellow  series.  White  is  considered  as  grade  16. 
Grading  has  been  done  by  comparison  with  standard  samples  of  hair, 
the  colors  of  which  are  defined  in  terms  of  Ridgway's  colors  at  the 
end  of  this  section. 

(3)  The  most  intense  grade  of  this  series  is  a  rich  dark  brown,  such 
as  is  found  hi  chocolate  guinea-pigs,  mice,  and  rabbits  and  in  liver- 
colored  dogs.  This  color  is  not  very  different  from  sepia4,  but  is  some- 
what warmer  and  less  dull.  As  noted  by  Miss  Durham  hi  the  case  of 
brown  mice,  there  seems  to  be  a  complete  absence  of  black  granules, 
but  a  large  quantity  of  brown  granules.  No  intergrades  between  this 
brown  and  black  are  known.  There  are  dilute  browns,  each  corre- 
sponding closely  to  a  color  hi  the  sepia  series.  They  are  often  difficult 
to  distinguish  from  grades  of  sepia  in  isolated  samples  of  hah*.  On  the 
animals,  however,  the  browns  seem  conspicuously  richer  than  the 
sepias.  There  are,  further,  correlated  differences  in  skin  and  eye  color 
which  are  even  more  conspicuous. 

Most  guinea-pig  colors  can  be  matched  fairly  well  in  the  sepia, 
brown,  or  yellow  series,  but  one  other  class  of  variations  must  be  noted. 
The  animals  have  been  graded  by  the  color  near  the  tip  of  the  hair,  but 
while  in  some  blacks,  sepias,  browns,  and  yellows  the  hah*  is  nearly 
uniform,  hi  most  cases  the  base  is  much  duller  than  the  tip.  This  gives 
a  somewhat  streaky  effect  to  the  fur.  In  the  case  of  dull  blacks  of  this 
kind,  the  color  at  the  base  of  the  fur  is  usually  between  a  neutral  slaty 
black  and  a  dark  sepia. 

SKIN  COLORS. 

The  color  of  the  skin  usually  corresponds  roughly  to  the  color  of  the 
hair  which  comes  from  it.  Where  the  fur  is  thick  there  is  very  little 
pigment  in  the  skin,  while  exposed  places  (as  ears  and  feet)  are  often 
very  strongly  pigmented. 

Where  the  fur  is  yellow  the  skin  in  exposed  places  shows  an  orange- 
yellow  color,  usually  with  considerable  admixture  of  black.  On  most 
of  the  body  the  skin  is  white,  with  occasional  orange-yellow  spots. 
The  dilution  of  fur  color  is  accompanied  by  dilution  of  the  skin  color. 

Where  the  fur  is  black  the  exposed  parts  of  the  skin  are  very  black, 
while  the  rest  of  the  skin  is  dull  black.  Where  the  fur  is  of  the  sepia 
series  the  color  of  the  ears  and  feet  depends  much  on  the  genetic  factors 
responsible  for  the  dilution  of  the  black.  In  the  sepias  of  the  albino 


62  INHERITANCE   IN   GUINEA-PIGS. 

series  the  ears  and  feet  are  quite  black,  often  with  intense  black 
blotches.  Even  in  albinos,  where  the  fur  is  nearly  pure  white,  the  ears 
and  feet  may  be  black.  In  the  pink-eyed  sepias,  on  the  other  hand, 
there  is  very  little  pigment  anywhere  in  the  skin. 

Brown  fur  goes  with  a  uniform  brown  color  of  ears  and  feet  very 
different  from  the  dull  black  of  sepias  of  corresponding  intensity  of 
fur  color.  Dilution  in  the  skin  accompanies  dilution  in  the  fur. 

The  different  skin  colors  are  very  conspicuous  in  animals  with 
spotted  fur.  In  these  it  is  easy  to  find  places  where  the  skin  spots  do 
not  correspond  exactly  to  the  fur  spots.  White  fur  may  arise  from 
colored  skin  and  yellow  fur  from  black  skin,  but  the  reverse  cases  do 
not  seem  to  occur. 

EYE  COLORS. 

The  iris  and  retina  usually  contain  black  and  brown  pigment. 
Where  there  is  reduction  of  pigment  in  the  iris,  the  pigment  tends  to 
disappear  first  next  to  the  pupil,  leaving  a  dark  outside  ring.  Decreas- 
ing grades  of  retinal  pigment  are  most  easily  recognized  by  the  apparent 
color  of  the  pupil.  In  black  eyes  the  pupil  appears  black.  Occasion- 
ally a  red  reflection  can  be  obtained  in  strong  light.  In  brown  eyes  a 
dark-red  reflection  is  easily  obtained  by  holding  the  guinea-pig  away 
from  the  light.  In  the  red  eye  the  pupil  looks  red  most  of  the  time 
and  the  inner  ring  of  the  iris  often  transmits  red  light.  A  pink  eye 
has  a  transparent  iris  and  a  pink  reflection  is  visible  through  both  iris 
and  pupil  in  all  lights. 

The  following  summary  shows  the  color  terms  to  be  used  in  this 
paper,  with  their  nearest  equivalent  on  Ridgway's  color  charts  (1912). 
The  numbers  15'i,  etc.,  refer  to  the  position  in  Ridgway's  system. 
For  purposes  of  convenience  in  defining  the  color  factors,  white  is 
included  as  a  member  of  each  color  series  as  well  as  in  a  class  by  itself. 
In  some  cases  white  may  be  shown  to  represent  extreme  dilution  of  a 
particular  color;  in  other  cases  it  stands  in  no  relation  to  particular 
colors. 

DEFINITION  OF  FUR  COLORS  BY  RIDGWAY'S  CHARTS. 

1 .  Pigment  absent  because  of  factors  not  belonging  to  a  dilution  series. 

White. 

2.  Pigment  present,  or  absent  only  because  of  factors  demonstrably  belonging 

to  a  dilution  series. 

a.  Yellow  group. 

Redo  =15%  ochraceous  tawny. 

Yellow3  =  16"6,  redder  than  cinnamon  buff,  17"6. 

Cream6  =  19"/,  cartridge  buff. 

White. 

b.  Dark  group. 

(1)  Black. 

Slaty  black  =  dark  neutral  gray. 

Blue  =  neutral  gray. 

White. 


COLOR.  63 

b.  Darfc'group — Continued. 

(2)  Black. 

Sepia3  =  16"'n,  warmer  and  darker  than  clove  brown,  17'"  m. 
Sepia6=16"%  warmer  and  lighter  than  clove  brown,  17"'  m. 
Sepia9  =  17'"%  hair  brown,  slightly  purer,  however. 
Sepial2  =  17""&,  light  drab,  somewhat  purer. 
Sepia15  =  17//"/,  pale  drab  gray,  somewhat  purer. 
White.        8^ 

(3)  Brown  =  15"  m,  bister,  15"m,  but  somewhat  wanner  and  duller. 
Brown3  =  15"%  between  army  brown,  13"%  and  buffy  brown,  17"'i. 
Brown6  =  17'"6,  somewhat  duller  than  avellaneous,  17"'&. 
Brown9=17""/? 

White. 

DEFINITIONS  OF  EYE  COLORS. 

(l)*Black:  black  iris  and  pupil. 

Dark  red :  black  iris,  dark-red  pupil  in  favorable  lights. 

Red :  partially  transparent  iris,  red  pupil  in  most  lights. 

Pink:  transparent  iris,  pink  reflection  through  both  iris  and  pupil. 
(2)  Brown:  brown  iris,  dark-red  pupil. 

Brown-red:  partially  transparent  brown  iris,  red  pupil. 

Pink :  as  above. 

HEREDITY  OF  FUR  AND  EYE  COLOR. 

COLOR  FACTORS  OF  GUINEA-PIGS. 

Considerable  work  has  been  done  on  the  inheritance  of  color  varia- 
tions in  guinea-pigs.  The  numerous  colors  which  have  been  listed  and 
several  patterns  in  which  these  colors  may  be  arranged  have  been  found 
to  be  due  in  the  main  to  relatively  few  hereditary  factors.  Some  of 
these  factors  determine  effects  which  are  very  easily  defined.  Thus, 
any  guinea-pig  which  is  homozygous  for  factor  Ca  is  an  albino  with  pink 
eyes  and  white  fur,  regardless  of  the  presence  of  any  combination  of 
other  known  factors.  On  the  other  hand,  certain  factors  determine 
nothing  except  in  combination  with  other  factors.  Factor  E  may  be 
present  in  guinea-pigs  of  any  known  color  variety  whatever.  It  can 
only  be  said  that  its  presence  is  a  necessary  condition  for  the  develop- 
ment of  more  than  a  trace  of  dark  pigmentation  in  the  fur.  The  color 
which  results  from  a  given  combination  of  factors  can  be  made  clear 
most  easily  by  classifying  the  factors  into  a  series  of  groups.  The 
following  classification  is  based  upon  the  factors  in  the  rodents  which 
have  been  most  studied,  viz,  guinea-pigs,  mice,  rats,  and  rabbits. 

CLASSIFICATION  OF  COLOR  FACTORS. 

1.  Factors  which  affect  the  distribution  and  intensity  of  color  largely  irre- 

spective of  the  kind  of  color. 

A.  Factors  which  govern  the  distribution  of  color  as  opposed  to  no  color 

(white)  in  patterns  in  the  fur,  in  individual  hairs,  and  in  the  eyes. 

B.  Factors  which  govern  the  intensity  of  general  color  development 

within  colored  areas  of  fur  and  eyes. 

2.  Factors  which  govern  the  differentiation  between  yellow  and  dark  colors 

in  colored  areas  of  the  fur. 

3.  Factors  which  determine  the  kind  of  dark  color  in  the  areas  with  dark 

pigmentation  in  fur  and  eyes,  without  influence  on  yellow  areas. 


64  INHERITANCE   IN   GUINEA-PIGS. 

COLOR  VS.  WHITE  (1  A). 

Probably  dilution  of  the  type  of  the  blue  and  dilute  yellow  mice  and 
rabbits  and  maltese  cats  belongs  here,  rather  than  in  IB,  since  the 
effect  seems  to  be  due  to  the  distribution  of  pigment  within  the  indi- 
vidual hairs  rather  than  to  any  effect  on  the  actual  pigment  granules. 
Most  of  the  factors  which  belong  hi  this  class,  however,  are  those  which 
determine  patterns  of  white  as  opposed  to  areas  which  are  colored 
under  most  combinations  of  other  factors.  In  this  class  are  such  fac- 
tors as  on  the  one  hand  determine  a  self-colored  coat,  and  on  the  other 
black-eyed  whites,  as  in  mice;  white  patterns,  as  in  hooded  rats,  Dutch 
and  English  rabbits;  or  scattered  white  hairs,  as  hi  silvered  guinea- 
pigs.  In  cases  where  several  independently  inherited  white  patterns 
have  arisen  it  is  evident  that  there  can  be  no  single  factor  which  alone 
determines  self.  The  "self  "  allelomorphs  of  the  white-pattern  factors 
can  merely  be  defined  as  conditions  for  self.  Where  more  than  one 
white-pattern  factor  is  present  in  an  animal,  combination  patterns  are 
produced. 

Clear-cut  Mendelian  factors  which  belong  to  this  group  are  known  in 
mice,  rats,  and  rabbits,  but  none  have  been  isolated  in  guinea-pigs, 
although  irregular  blotching  and  silvering  with  white  are  common.  The 
symbol  S  will  be  used  to  represent  an  assemblage  of  unanalyzed  factors. 

Stc,  an  assemblage  of  unanalyzed  factors  which  determine  white  spotting. 
INTENSITY  OF  GENERAL  COLOR  DEVELOPMENT  (1  B). 

In  this  group  fall  albinism  and  its  variations.  These  factors  affect 
all  color,  but  not  wholly  irrespective  of  the  kind  of  color.  There  are 
several  peculiarities  which  are  discussed  more  fully  in  a  later  section 
(page  70).  The  most  important  is  the  fact  that  the  level  of  intensity 
of  the  color  factor  at  which  yellow  can  develop  at  all  is  higher  than  the 
threshold  for  black  or  brown.  This  does  not  affect  the  differentiation 
of  the  fur  into  yellow  and  dark  pigmentation  areas  by  factors  of  group 
2,  but  involves  the  result  that  with  certain  albino  series  factors,  yellow 
areas  appear  white,  while  dark  areas  are  quite  strongly  colored.  Indeed, 
in  albinism  itself,  dark  pigmentation  areas  can  often  be  distinguished 
from  yellow  areas  by  a  slight  sootiness  in  the  former,  absent  in  the  latter. 

C.  Determines  the  highest  intensity  of  color  of  skin,  fur,  and  eye  which  is  to  be  found  with  a 
given  array  of  other  factors;  dominant  over  Ca,  CV,  and  Ca,  where  distinguishable 
in  its  effects.  In  the  following  table,  and  hi  the  similar  tables  under  Cd,  CV,  and  Ca, 
are  given  the  ranges  of  intensity  in  the  yellow,  black,  and  brown  series  to  which 
these  colors  develop  when  the  factor  under  consideration  is  present.  In  the  case 
of  black  and  brown,  factor  P  is  assumed  to  be  present.  When  p  is  present,  black 
and  brown  undergo  a  two-fold  dilution.  P  is  also  considered  present  in  the  case 
of  eye-color. 

Yellow  series — redo  to  yellow2  in  guinea-pigs;  yellows  to  creams  in  Cavia 
cutleri. 

Black  series — blacko  to  black2. 

Brown  series — browno  to  brown2- 

Eye  color — black,  brown. 


COLOR.  65 

Cd'  Determines  an  intensity  of  yellow  distinctly  lower  than  does  C,  an  intensity  of  dark  pig- 
mentation usually,  but  not  always  lower  than  does  C,  and  an  intensity  of  eye  color 
rarely  distinguishable  from  that  determined  by  C.  More  or  less  dominant  over 
Cr  and  Ca  where  distinguishable.  (Wright,  1915.) 

Yellow  series — yellow2  to  creamy. 

Black  series — blacko  to  sepiay. 

Brown  series — browno  (?)  to  brown? . 

Eye  color — black,  brown. 

Cr.  Determines  the  complete  absence  of  yellow,  an  intensity  of  dark  pigmentation  indis- 
tinguishable from  that  determined  by  Cd  and  an  intensity  of  eye  color  lower  than 
that  determined  by  C  or  Cd-  More  or  less  dominant  over  Ca  where  distinguish- 
able. (Castle,  1914o;  Wright,  1915.) 

Yellow  series — white. 

Black  series — blacko  to  sepias . 

Brown  series — browno  (?)  to  browny. 

Eye  color — red,  brown-red. 

C0.  Determines  an  absence  of  pigment,  complete  with  yellow,  not  quite  complete  with 
dark  pigments  of  the  fur  and  skin,  but  complete  in  the  eyes.  (Castle  and  Allen, 
1903;  Castle,  1905;  Sollas,  1909;  Detlefsen,  1914;  Wright,  1915.) 

Yellow  series — white. 

Black  series — white,  dark  smudges  on  nose,  ears,  and  feet. 

Brown  series — white,  brown  smudges  on  nose,  ears,  and  feet. 

Eye  color — pink. 

DARK  VS.  YELLOW  COLOR  (2). 

Factors  of  this  group  affect  skin  and  fur  color,  but  not  eye  color.  In 
this  group  come  the  factors  responsible  for  self  yellows,  tortoise-shells, 
and  brindles,  on  the  one  hand,  and  self  blacks  or  browns  on  the  other, 
as  contrasted  with  the  ticked  or  agouti  patterns  of  the  wild  rodents. 
Where  more  than  one  factor  is  present  which  determines  a  yellow 
pattern,  combination  effects  are  produced,  such  as  in  yellow-spotted 
agoutis  among  guinea-pigs.  The  following  factors  are  known  in  guinea- 
pigs: 

E.  A  condition  for  more  than  a  trace  of  dark  pigmentation  in  the  fur;  determines  dark  pig- 
mentation wherever  yellow  is  not  determined  by  other  factors;  dominant  over  e, 
found  in  the  wild  species,  all  agoutis,  blacks,  browns,  etc.,  but  very  rarely  in  self 
yellows. 

«.  Determines  the  presence  of  one  of  the  yellow  colors  in  all  colored  areas  of  the  fur,  aside 
from  a  slight  sootiness;  responsible  for  the  yellow  in  most  self  yellows,  for  the  white 
in  red-eyed  whites,  etc.  (Castle,  1905, 1907, 1907o;  Sollas,  1909;  Detlefsen,  1914.) 

A.  Determines  the  presence  of  a  yellow  color  in  the  light-bellied  agouti  pattern  wherever 
there  is  dark  pigmentation  in  which  the  yellow  group  ticking  may  show;  dominant 
over  A'  and  a,  found  in  Cavia  cutteri  and  light-bellied  agouti  guinea-pigs,  includ- 
ing the  red-eyed  silver  agoutis,  in  which  the  agouti  pattern  is  in  white. 

A'.  Determines  the  presence  of  yellow  colors  in  a  more  restricted  agouti  pattern  than  does  A, 
a  pattern  usually  characterized  by  a  ticked  belly  not  sharply  distinct  from  the 
sides  in  color;  dominant  over  a,  found  hi  Cavia  rufescens  and  in  ticked-bellied  agouti 
hybrids  which  have  rufescens  ancestry.  (Detlefsen,  1914.) 

a.  Determines  the  absence  of  yellow  group  ticking  in  hairs  of  dark  pigmentation;  found  in 
blacks,  browns,  etc.  (Castle,  1905,  1907,  1907a,  1913;  Sollas,  1909;  Detlefsen, 
1914.) 

Zy.  An  assemblage  of  unanalyzed  factors  which  determine  the  presence  of  spots  of  a  yellow 
color,  conditional  on  factors  of  group  (1) ;  found  in  black  and  yellow  tortoise-sheila, 
black,  yellow,  and  white  tricolors,  and  in  some  red-eyed  black  and  white  bicolors; 
probably  responsible  for  an  occasional  self  yellow,  though  never  in  the  writer's 
experience. 


66  INHERITANCE   IN   GUINEA-PIGS. 

VARIATIONS  OF  DARK  COLOR  (3) 

Factors  of  this  group  are  responsible  for  browns  and  pink-eyed 
sepias,  as  compared  with  blacks,  hi  guinea-pigs;  for  browns  and  pink- 
eyed  sepias  in  mice,  and  for  the  new  pink-eyed  and  red-eyed  dilute 
variations  hi  rats.  Where  more  than  one  factor  of  this  group  or  of 
group  IB  determines  dilution,  combination  effects  are  produced.  Thus 
we  have  very  pale  sepias  resulting  from  the  combined  effects  of  two 
independent  dilution  factors  (CdCdpp). 

B.  Determines  a  color  of  the  black-sepia  series  wherever  dark  pigmentation  develops, 
including  the  eyes;  has  no  influence  where  yellow  pigmentation  develops;  domi- 
nant over  b,  present  in  the  wild  species  and  in  blacks,  sepias,  albinos  with  black 
points,  black-eyed  yellows,  etc. 

b.  Determines  a  color  of  the  brown  series  wherever  dark  pigmentation  develops,  including 
the  eyes;  has  no  influence  where  yellow  pigmentation  develops;  present  in  browns, 
brown-eyed  yellows,  etc.  (Castle,  1907o,  1908;  Sollas,  1909;  Detlefsen,  1914.) 

P.  A  condition  for  intense  development  of  dark  pigmentation  in  the  fur  and  for  eye  colors 
more  intense  than  pink;  not  necessary  for  intense  development  of  yellow;  domi- 
nant over  p. 

p.  Determines  a  low  development  of  dark  colors,  i.  e.,  below  sepias;  has  no  influence  where 
yellow  develops;  determines  pink  eye  color.  (Castle,  1914o.) 

TABLE  OF  FACTOR  COMBINATIONS. 

In  determining  the  color  which  corresponds  to  a  given  array  of  factors 
the  groups  of  factors  must  be  considered  in  the  order  given.  Table  33 
gives  a  list  of  the  color  varieties  corresponding  to  the  combinations  of 
Mendelian  factors.  At  the  top  and  left  of  the  table  are  indicated,  by 
symbols,  the  factors  present  in  each  of  the  varieties  named  in  the  body 
of  the  table.  The  color  of  spots  produced  by  Sw  and  Sy  are  given 
below.  Only  the  varieties  marked  with  an  asterisk  have  not  yet  been 
synthesized.  These  include  the  pink-eyed  yellows  and  creams  and  a 
kind  of  pink-eyed  white  which  is  expected  to  be  indistinguishable  from 
an  albino  in  appearance,  though  breeding  wholly  differently.  The  pink- 
eyed  brown  series  (bbpp)  has  not  yet  been  produced  and  is  not  included. 
Some  of  the  varieties  have  names  given  by  fanciers  which  have  been 
used  in  the  literature.  In  this  table,  however,  it  seemed  best  to  use  a 
consistent  scheme  of  naming,  indicating  at  once  the  color  and  pattern. 
Agouti  is  used  as  the  name  for  a  pattern,  the  banding  of  hairs  of  pre- 
dominantly a  dark  color  with  a  yellow  color.  The  names  preceding 
agouti  give  the  two  colors  in  each  hair.  The  following  table  of  syno- 
nyms may  be  useful: 

Black-red  agouti  =  golden  agouti. 

Sepia-yellow  agouti  =  yellow  agouti. 

Sepia-cream  agouti  =  silver  agouti. 

Brown-red  agouti  =  cinnamon. 

Brown-cream  agouti  =  light  cinnamon. 

Sepia  =  blue.  '  ^* 

Brown  =  chocolate. 

Brown  eye= brown  eye  (Castle),  ruby  eye  (Sollas). 


COLOR. 
TABLE  33. 


67 


Factors 

Fur. 

Eve 

present. 

EA   (agouti  light-belly). 
EA'  (agouti  ticked-belly). 

Eaa. 

ee  (A,  A'  or  aa)  . 

B  PC 

Black-red  agouti       

Black  

Red  

Black. 

CdCd 

Dark  sepia-yellow  agouti  

Dark  sepia  .... 

Yellow  

Do. 

CdCr 

Dark  sepia-cream  agouti  . 

Do  

Cream  

Do. 

CnCa 

Light  sepia-cream  agouti 

Light  sepia  .... 

...  Do  

Do. 

CrCr 

Dark  sepia-white  agouti 

Dark  sepia  

White   (light 

Red. 

Light  sepia-white  agouti 

Light  sepia  

points)  . 
Do  

Do 

CaCft 

^^hite  (dark  points) 

White   (dark 

Do     

Pink 

Bpp  C 

Pale  sepia-red  agouti    

points)  . 
Pale  sepia  

Red  

Pink. 

CdCd 

Very  pale  sepia-yellow  agouti 

Very  pale  sepia  . 

*Yellow  

Do. 

CrlCr 

Very  pale  sepia-cream  agouti. 

.  .  Do         ... 

*Cream                 .  . 

Do 

CdCa.  • 

...  Do  

Do  

...*Do  

Do. 

CrCr 

Very  pale  sepia-white  agouti 

.Do  

*White 

Do 

..  .Do  

Do  

..  .*Do  

Do. 

C  C 

White  (light  points)  

White    (light 

...*Do  

Do. 

bbP  C 

Brown-red  agouti         .    . 

points). 
Brown 

Red 

Brown 

CdCd  •  • 

Medium  brown-yellow  agouti  . 

Medium  brown  . 

Yellow  

Do. 

CaCr.    . 

Medium  brown-cream  agouti  . 

Do  

Cream  

Do. 

CdCa.  • 

Light  brown-cream  agouti  .... 

Light  brown.  .  .  . 

Do  

Do. 

CrCr 

Medium  brown-white  agouti  .  . 

Medium  brown  . 

White  

Brown-red  . 

Light  brown-white  agouti  .    .  . 

Light  brown  .  .  . 

Do  

Do. 

C1  (~* 

White  (It.  br.  points)    

White    (It.    br. 

.  Do   . 

Pink. 

points). 

Factors 
present. 

Sw. 

Sy. 

SwSy. 

Eye. 

c 

W^hite  spots  (clear)           .  . 

Red  spots  . 

Red  and  white  tri- 

CdCd •  • 

Do  

Yellow  spots  .  .  . 

color. 
Yellow  and  white. 

CdCr.  .  . 

Do  

Cream  spots  .... 

Cream  and  white 

CdCa  .  - 

.  .Do  

Do  

tricolor. 
Do  

CrCr... 

.    .Do  

\White  spots, 

Sooty  and  clear, 

.Do  

/    often  sooty. 

white  spots. 

(Albino)  

(Albino)  

(Albino)  

HEREDITARY  FACTORS  AND  THE  PHYSIOLOGY  OF  PIGMENT. 

The  definitions  which  have  been  given  for  the  hereditary  factors  are 
based  largely  on  the  colors  as  seen  without  a  microscope.  It  would  be 
very  desirable,  however,  to  correlate  color  factors  accurately  with  the 
variations  in  quality  and  quantity  of  the  actual  pigments  and  ultimately 
with  the  physiology  and  chemistry  of  pigment  formation. 

Considerable  progress  has  been  made  in  recent  years  in  the  study  of 
the  chemistry  of  melanin  pigments.  The  melanins  are  amorphous 
granular  pigments  found  throughout  the  animal  kingdom.  A  large 
number  of  researches  have  established  the  fact  that  substances  which 
closely  resemble  the  natural  melanins  can  be  produced  by  the  action  of 


68  INHERITANCE   IN    GUINEA-PIGS. 

certain  oxidizing  enzymes  on  tyrosin  and  related  aromatic  compounds. 
Tyrosin  is  an  important  constituent  of  protein  molecules  and  there  is 
much  reason  to  believe  that  tyrosin  and  related  substances  are  the 
chromogens  from  which  the  natural  melanins  are  formed.  Tyrosinase, 
an  enzyme,  which  can  oxidize  tyrosin  to  dark  substances  resembling 
melanins,  has  been  found  very  widely  among  animals,  including  the 
skins  of  mammals,  as  will  be  discussed  later. 

There  have  been  many  theories  on  the  mode  of  origin  of  pigment  hi 
the  cells.  Early  observations  indicated  that  melanin  was  directly 
extruded  from  the  nucleus.  Recent  studies  by  Hooker  (1915)  on  in 
vitro  cultures  of  mesenchyme  and  epithelium  of  the  frog  indicate  that 
melanin  granules  form  in  the  cytoplasm  but  at  the  point  of  known 
greatest  efficiency  of  the  nucleus  as  an  oxidizing  agent.  Thus,  prob- 
ably chromogen  (tyrosin  or  derivatives)  is  in  the  cytoplasm,  while 
oxidizing  enzymes  are  given  off  by  the  nucleus. 

The  color  white  in  the  fur  of  mammals  is  due  to  the  absence  of 
pigment.  The  theory  of  a  white  melanin  seems  effectively  disproved 
(Gortner,  1910).  A  priori,  the  presence  or  absence  of  pigment  might 
be  conceived  as  due  either  to  a  deficiency  of  chromogen  or  of  enzyme. 
In  line  with  the  first  view,  Gortner  (1911)  found  that  the  pattern  in 
the  elytra  of  potato  beetles  is  due  to  a  deficiency  of  chromogen.  Fur- 
ther, Cue"not  (1903,  1904),  hi  the  first  attempt  to  correlate  the  facts  of 
Mendelian  inheritance  with  the  physiology  of  pigment,  suggested  pro- 
visionally that  albinos  lack  the  power  of  producing  chromogen,  while 
the  different  colors  which  he  demonstrated  could  be  transmitted 
through  albinos  depend  on  specific  enzymes.  On  the  other  hand, 
recent  observations  by  Onslow  (1915)  demonstrate  that  absence  of 
pigment  in  widely  different  cases  in  mammals  depends  on  enzyme  differ- 
ences. He  found  peroxidases  hi  the  skins  of  gray,  black,  blue,  and 
brown  rabbits,  which  produce  a  black  pigment  from  tyrosin  in  the 
presence  of  hydrogen  peroxide.  In  the  skins  of  albino  rabbits  and  mice 
and  in  the  white  part  of  the  Dutch  pattern  in  rabbits,  all  recessive 
whites,  he  was  unable  to  demonstrate  a  peroxidase,  although  there  was 
nothing  present  which  prevented  the  oxidation  of  tyrosin  to  a  black 
pigment  when  tyrosinase  was  added.  In  the  white  of  the  English 
rabbit,  a  dominant  white,  he  did  find  an  anti-tyrosinase. 

Finally,  there  is  strong  genetic  evidence  that  albinism  in  guinea-pigs 
is  not  due  to  absence  of  chromogen.  A  diminution  in  quantity  of 
chromogen  should  bring  about  the  same  diminution  hi  quantity  of  all 
pigments,  regardless  of  quality.  But  hi  red-eyed  guinea-pigs  (which 
we  may  consider  as  incomplete  albinos,  as  they  have  an  allelomorph 
of  albinism  Cr)  no  yellow  develops,  leaving  white  areas  where  factors 
of  group  2  determine  yellow  differentiation,  but  there  may  be  nearly 
as  much  black  as  hi  normal  guinea-pigs.  Indeed,  hi  the  albino  guinea- 
pigs  and  Himalayan  rabbits,  there  is  no  yellow,  but  some  black. 


COLOR.  69 

The  physical  or  chemical  differences  between  the  pigments  of  the 
different  fur  colors  are  not  wholly  clear.  According  to  Onslow  (1915) 
the  pigments  of  black,  brown,  and  yellow  rabbits  can  not  be  distin- 
guished, physically  or  chemically,  when  isolated.  At  first  sight  this 
seems  hardly  possible  with  such  apparently  different  colors.  A  result 
thoroughly  in  line  with  this  view,  however,  followed  the  matching 
of  fur  colors  with  Ridgway's  charts,  much  to  the  writer's  surprise  at 
the  time.  Ridgway  distinguishes  72  hues  passing  from  red  through 
orange,  yellow,  green,  blue,  and  purple,  back  to  red.  The  yellows, 
sepias,  and  browns  of  guinea-pigs  and  human  brown  and  red  hair  all 
matched  colors  near  hue  17,  "orange  yellow,"  in  the  classification. 
The  differences  depended  merely  on  differing  amounts  of  black  and 
white.  Bateson  (1903),  indeed,  found  that  yellow  pigment  is  dissolved 
from  hair  by  potassium  hydroxide  very  much  more  rapidly  than  brown 
pigment,  which  dissolved  more  rapidly  than  black.  This,  however, 
might  be  due  merely  to  size  or  density  of  granules. 

This  apparent  qualitative  difference  in  pigments  has  been  attributed 
to  several  causes:  (1)  to  variations  hi  the  chromogen  acted  on  by  a 
given  enzyme,  (2)  to  interruptions  at  different  stages  in  the  process  of 
oxidation  of  a  given  chromogen,  (3)  to  specific  enzymes  which  in  each 
case  can  only  produce  a  certain  result  once  the  action  on  the  chromo- 
gen is  begun. 

Observations  of  Onslow  indicate  that  for  qualitative  differences,  as 
well  as  for  the  absence  of  pigment,  enzyme  and  not  chromogen  differ- 
ences are  responsible.  He  could  find  no  peroxidase  in  self  yellows,  a 
recessive  variation.  There  must  of  course  have  been  some  peroxidase 
at  some  time  to  produce  pigment  at  all.  Perhaps  the  apparent  absence 
indicates  a  very  low  degree  of  stability  in  the  yellow-producing  enzyme. 
Again,  grays  differ  from  blacks  by  a  dominant  factor  which  causes 
yellow  to  appear  in  ticking  over  the  back  but  white  to  appear  on  the 
belly.  Onslow  found  a  tyrosinase  inhibitor  in  the  belly  and  compared 
the  case  with  that  of  the  dominant  white  of  the  English  rabbit.  As 
grays  differ  from  self  blacks  by  only  one  Mendelian  factor,  it  would 
seem  likely  that  all  of  the  changes  in  appearance — dorsal  yellow  tick- 
ing, ventral  white — are  to  be  ascribed  to  one  physiological  cause.  If 
black  is  absent  from  the  belly  because  of  an  enzyme  inhibitor,  it  would 
seem  likely  that  black  is  replaced  by  yellow  in  the  dorsal  ticking  by  the 
presence,  for  a  certain  period  hi  the  development  of  a  hair,  of  the  same 
enzyme  inhibitor,  which,  however,  is  in  this  case  merely  an  inhibitor  of 
the  black-producing  reaction,  not  of  the  yellow.  Reasons  for  which 
yellow  can  appear  on  the  back  of  rabbits,  but  not  on  the  belly,  when 
black  is  inhibited  will  be  discussed  later.  Thus,  a  recessive  yellow  and 
a  dominant  yellow-pattern  factor  are  both  due  to  enzyme,  not  chromo- 
gen, differences. 


70 


INHERITANCE    IN   GUINEA-PIGS. 


The  second  hypothesis — that  yellow,  brown,  and  black  are  due  to 
interruptions  of  the  normal  process  of  oxidation  at  different  stages  is 
difficult  to  reconcile  satisfactorily  with  the  genetic  facts  in  guinea-pigs. 
If  brown  and  black  pigments  pass  through  a  yellow  stage,  identical 
with  the  final  stage  of  the  pigment  in  yellow  guinea-pigs,  any  factor 
which  inhibits  the  development  of  yellow  must  a  fortiori  inhibit  the 
development  of  brown  and  black.  We  have  seen  that  with  factor  Cr 
there  is  complete  absence  of  yellow  pigment,  but  nearly  full  develop- 
ment of  brown  and  black.  We  find  nearly  the  converse  of  this  in  the 
effect  of  factor  p.  When  factor  p  is  present,  the  development  of 
brown  and  black  is  very  greatly  reduced  without  the  slightest  dilution 
of  yellow.  This  indicates  that  neither  is  yellow  a  stage  in  the  develop- 
ment of  black  nor  black  a  stage  in  the  development  of  yellow.  The 
most  satisfactory  hypothesis  is  the  third — that  there  are  distinct 
enzymes  which  produce  yellow  and  dark  pigment. 

There  are  a  number  of  curious  facts  hi  connection  with  the  albino 
series  of  factors  in  guinea-pigs  which  perhaps  warrant  further  specula- 
tion. As  has  been  mentioned,  Onslow  has  shown  that  albinism  is  due 
to  the  absence  of  tyrosinase  hi  the  skin  (and  presumably  the  eye).  It 
seems  reasonable  to  suppose  that  the  higher  allelomorphs  are  quantita- 
tive variations  in  a  factor  which  determines  the  power  of  producing 
tyrosinase.  If  this  is  so,  we  would  expect  to  find  that  the  different 
zygotic  formulae  could  be  arranged  in  a  linear  series  with  respect  to 
their  effects  on  pigments  of  all  sorts.  Following  are  the  series  with 
respect  to  black  pigment  of  eye  and  fur,  and  yellow  of  the  fur.  (See 
plates  1  and  2.) 


Formula. 

Black  eye. 

Black  fur. 

Yellow  fur. 

cc  

Black  .... 

Black  

Red. 

CCd  

...  Do  

Do  

Do. 

CCr  

..  Do  .... 

Do  

Do. 

CCa  .  .  . 

.Do  .... 

Do  

Do. 

CdCd  .  . 

.Do  .... 

Dark  sepia  

Yellow. 

CdCr  

.  ..Do  

Do  

Cream. 

CdCa  

...  Do  

Light  sepia  

Do. 

CrCr 

Red 

Dark  sepia  .  .  . 

White. 

CrCa  

..Do  

Light  sepia  

Do. 

CaCa  

Pink  

White  (sooty)  .  .  . 

Do. 

The  yellow  series  and  the  less  accurately  known  eye-color  series  can 
be  arranged  in  the  same  sequence.  There  is  the  striking  difference, 
however,  that  the  level  of  no  pigment  production  is  much  higher  in 
yellow  than  eye  color.  The  black  of  the  fur  agrees  with  eye  color  in 
the  level  at  which  pigmentation  becomes  evident — between  CaCa  and 


COLOR.  71 

CrCa — but  the  sequence  can  not  be  made  to  agree  with  either  the  eye- 
color  or  yellow  series.  CaCa  is  distinctly  lighter  than  CrCr  in  black 
fur  but  distinctly  more  intense  in  eye  color  while,  hi  yellow  fur  CaCa 
is  above,  CrCr  below  the  threshold  of  any  color.  The  effects  could  be 
explained  by  a  complicated  linkage  hypothesis.  We  would  need  to 
suppose  that  there  are  separate  series  of  allelomorphs  acting  on  yellow, 
black  of  fur,  and  black  of  eye,  respectively,  and  that  Cr  and  Ca  are 
complexes  identical  hi  the  yellow-dilution  factor,  Cd  and  Cr  identical 
in  the  black-fur-dilution  factor  and  perhaps  C  and  Cd  hi  the  black-eye- 
dilution  factor.  But  an  hypothesis  according  to  which  it  is  a  mere 
accident  that  the  factors  which  dilute  yellow,  black  of  fur,  and  black 
of  eye  are  perfectly  linked  in  inheritance  can  hardly  be  taken  seriously. 
Another  escape  would  be  to  suppose  that  our  four  factors,  Ca,  Cr,  Cd, 
and  C,  are,  indeed,  variations  of  the  same  thing  but  not  linear  quantita- 
tive variations.  However,  it  seems  most  satisfactory  to  the  writer  to 
attempt  to  explain  the  results  on  the  basis  of  four  quantitative  gradations 
of  one  factor,  which  determines  the  amount  of  the  basic  color-producing 
enzyme,  if  it  is  in  any  way  possible.  Let  us  see  what  assumptions 
must  be  made  to  do  this.  First,  it  will  be  convenient  to  assume  with 
Little  (1913)  that  the  basic  color-producing  enzyme  (I)  acting  by 
itself  on  chromogen,  produces  yellow  pigment.  The  addition  of  a 
second  substance  (II)  makes  it  a  black-producing  enzyme  (I-II).  We 
will  further  assume  that  I  is  relatively  unstable  and  must  be  produced 
above  a  certain  rate  (that  determined  by  CrCr)  in  order  to  reach  and 
oxidize  the  chromogen  in  the  cytoplasm.  United  with  II  it  becomes 
more  stable  and  even  produces  some  effect  at  the  rate  of  production 
determined  by  CaCa.  The  next  assumption  is  that  above  the  thresh- 
old for  yellow,  I-II  and  the  excess  of  I  compete  for  the  chromogen. 
As  a  result  of  partial  displacement  by  the  paler  color,  the  intensity  of 
black  decreases  just  above  the  yellow  threshold.  CdCa  seems  paler 
(and  somewhat  browner)  than  CrCr.  In  the  eye,  no  factor  ever 
brings  out  a  yellow  color.  There  is  perhaps  never  an  excess  of  I  here 
and  the  intensity  of  black  follows  the  normal  sequence. 

Summarizing,  the  hypothesis  to  which  consideration  of  the  physio- 
logical and  genetic  seems  to  lead  is  as  follows : 

(1)  There  is  a  basic  color-producing  enzyme  (I)  which  acting  alone 
on  chromogen  produces  a  diffuse  or  finely  granular  pigment  which 
appears  yellow.    It  is  relatively  unstable.     Intensity  of  production 
and  absence  or  inhibition  in  parts  of  fur  and  eye  are  determined  by  the 
various  factors  of  group  1 — the  albino  series,  "  blue  "-dilution  factors, 
and  recessive  and  dominant  white-pattern  factors. 

(2)  There  is  a  second  substance  (II)  which  may  unite  with  I  to 
produce  a  more  stable  enzyme,  which  reacts  with  chromogen  to  produce 
a  coarsely  granular  pigment  which  appears  sepia,  brown,  or  black. 
When  II  is  present,  I  is  stabilized  to  such  an  extent  that  pigment  is 


72  INHERITANCE   IN   GUINEA-PIGS. 

produced  at  a  lower  rate  of  production  of  I  than  is  the  case  of  I 
alone.  Above  the  level  at  which  I  alone  produces  yellow,  the  two 
kinds  of  enzymes,  yellow-  and  black-producing,  compete  with  each 
other  for  chromogen,  producing  a  mixture  of  black  and  yellow,  the 
relative  importance  depending  on  the  rate  at  which  II  is  produced. 
Because  of  the  competition  the  intensity  of  black  shows  two  maxima 
as  production  increases — one  just  below  the  yellow  threshold  and  the 
other  at  maximal  production  of  I.  Intensity  of  production  or  inhibi- 
tion of  II  in  patterns  hi  the  fur  are  determined  by  various  factors 
(group  2)  which  produce  self  yellow,  yellow  spotting,  agouti,  etc. 

(3)  There  is  a  third  group  of  substances  which,  added  to  the  dark- 
pigment-producing  enzyme  (II),  affect  the  intensity  of  dark  color  pro- 
duced but  not  the  power  of  fixing  chromogen  in  competition  with  the 
yellow-producing  enzyme.  They  have  no  effect  on  the  intensity  of 
yellow.  In  this  group  are  the  brown  factors  of  mice  and  guinea-pigs, 
and  perhaps  rabbits  and  dogs,  the  pink-eye  factor  of  rats,  mice,  and 
guinea-pigs  and  the  new  red-eye  factor  of  rats,^.e.,  the  factors  of  group  3. 

While  based  to  a  larger  extent  on  the  genetic  facts  in  the  albino 
series  in  guinea-pigs,  the  hypothesis  explains  many  cases  in  other 
mammals  in  the  sense  that  apparently  complex  variations  are  reduced 
to  a  single  physiological  cause. 

In  rabbits,  single  Mendelian  factors  produce  some  rather  complex 
variations.  A  single  factor  changes  a  self  black  to  the  gray  color  with 
a  yellow-ticked  back  but  a  pure  white  belly.  Another  variation 
changes  a  self  black  to  a  sooty  yellow  with  a  black  belly.  These  varia- 
tions combined  hi  one  animal  give  a  white-bellied  clear  yellow.  How 
can  each  of  these  apparently  complex  color  changes  be  determined  by 
a  simple  physiological  change?  Let  us  suppose  that  in  all  rabbits  I 
is  produced  strongly  on  the  back,  but  so  feebly  on  the  belly  that  it  is 
below  the  yellow  threshold,  but  not  so  feebly  that  black  is  greatly 
affected.  Let  us  suppose  that  II  is  likewise  more  strongly  produced 
on  back  than  on  belly.  A  factor  which  tends  to  produce  an  inhibitor 
of  II  is  added.  On  the  back  II  (the  black-producing  enzyme)  is 
inhibited  in  only  a  portion  of  the  development  of  the  hair,  leaving 
yellow  ticking.  On  the  belly  all  II  is  inhibited,  leaving  white.  The 
result  is  a  gray  rabbit.  The  other  factor  causes  a  general  slowing  up 
in  the  production  of  II.  On  the  back  this  enables  the  yellow-pro- 
ducing enzyme  to  predominate  in  competition  and  sooty  yellow  results. 
On  the  belly — below  the  yellow  threshold — what  little  black-producing 
enzyme  does  develop  has  no  competition  and  only  black  can  result. 
We  get  a  black-bellied  sooty  yellow.  The  combination  pattern  can 
only  be  a  white-bellied  yellow.  In  many  other  mammals  color  phases 
are  found  which  can  be  explained  as  due  either  to  variations  in 
production  of  II  or  I.  The  red  phase  of  the  red  fox,  has  a  white 
chest.  The  level  of  production  of  I  is  below  the  yellow  threshold 


COLOR.  73 

but  above  the  black  threshold  on  the  chest.  Increase  in  production 
of  II  produces  the  silver  phase,  nearly  self  sepia  in  color,  including 
the  chest.  The  colors  of  the  varying  hare  seem  to  be  due  to  variations 
in  production  of  I  determined  by  environmental  causes.  The  white 
winter  pelage  gives  way  in  blotches  to  a  white-ticked  sepia;  this  gives 
way  to  yellow-ticked  sepia  as  the  intensity  of  production  of  the  basic 
enzyme  rises  above  the  yellow  threshold  and  in  some  varieties  the  full 
summer  pelage  is  almost  self  red. 

Many  other  cases  could  be  given  in  which  two  color  phases  of  an 
individual  animal  or  the  color  patterns  of  closely  allied  varieties  seem 
to  differ  in  many  respects  and  yet  can  be  explained  on  the  basis  outlined 
as  due  to  a  single  physiological  change. 

In  the  case  of  very  complex  color  patterns,  it  is  necessary  to  suppose 
that  the  power  of  producing  the  hypothetical  enzymes  I,  II,  or  III 
may  be  distributed  in  quite  complex  patterns.  But  the  hypothesis 
often  gives  a  simple  explanation  for  certain  peculiarities  in  a  pattern. 
In  the  tiger,  the  stripes  on  the  back  are  quite  intense  yellow  and  black. 
The  yellow  stripes  grow  paler  down  the  sides,  becoming  white  on  the 
lower  sides  and  belly.  The  black  stripes  likewise  grow  lighter  down 
the  sides  but  at  the  point  at  which  the  yellow  becomes  white,  the  black 
stripes  suddenly  grow  more  intense,  at  least  in  some  individuals,  to 
become  paler  again  on  the  belly.  Again,  on  the  legs,  which  are  white 
on  the  inside,  yellow  on  the  outside,  black  stripes  are  visible  on  the 
white  part,  but  either  disappear  completely  or  leave  merely  a  streak  of 
sooty  red  on  the  yellow  part.  All  of  this  becomes  intelligible  if  we 
assume  that  the  basic  enzyme  (I)  is  produced  at  decreasing  rates  from 
back  to  belly  and  from  outside  to  inside  of  leg,  while  the  black-produc- 
ing supplement  (II)  is  distributed  in  vertical  stripes  (horizontal  on  the 
legs).  Two  parallel  stripes  give  a  remarkable  reproduction  of  the 
variation  hi  black  and  yellow  in  the  albino  series  in  guinea-pigs.  We 
have  the  same  change  from  black  and  intense  yellow  to  sepia  and 
cream,  then  to  darker  sepia  and  white,  and  finally  light  sepia  and  white, 
illustrating  the  different  thresholds  for  the  appearance  of  black  and 
yellow  and  the  reduction  in  intensity  of  black  above  the  yellow  threshold 
due  to  the  entrance  of  competition  at  this  point. 


DISCUSSION  OF  EXPERIMENTS. 

MATERIAL. 
SYSTEMATIC  POSITION. 

Guinea-pigs  belong  to  the  family  Caviidse  of  the  hystricomorph 
division  of  rodents.  There  are  three  living  genera  of  Caviidse:  Doli- 
chotis  Desm.,  which  contains  the  large  Patagonian  cavies;  Hydrochcerus 
Brisson,  to  which  belongs  the  capybara;  and  Cavia  Pallas,  containing 
the  small  cavies.  Genus  Cavia  is  divided  into  two  subgenera,  Cavia 
proper  and  Cerodon  F.  Cuv.,  distinguished  most  conspicuously  by  the 
greater  complexity  of  the  molars  hi  the  former.  Seven  living  species 
are  listed  under  Cavia  proper  by  Trouessart  (1904)  : 

C.  rufescens  Lund,  a  small  dark  Brazilian  cavy  with  subspecies  in  Guiana  and 

Argentina. 
C.  fidgida  Wagler,  a  Brazilian  cavy  probably  closely  allied  to  rufescens  (Thomas, 

1901). 

C.  aperea  ErxL,  a  large  pale-colored  Brazilian  cavy. 
C.  azarce  Wagner,  a  cavy  of  Paraguay  probably  closely  allied  to  aperea  (Thomas, 

1901). 

C.  cutleri  Bennett,  a  small  pale-colored  cavy  of  Peru. 
C.  tschudii  Fitzinger,  a  large,  richly  colored  cavy  described  from  lea,  Peru. 
C.  porcellus  Linn.,  the  tame  guinea-pig,  much  larger  than  at  least  rufescens  and 

cutleri. 

DESCRIPTION  OF  STOCKS. 

Four  of  these  species  are  dealt  with  hi  the  experiments  to  be  described, 
viz,  Cavia  rufescens,  C.  cutleri,  C.  porcellus,  and  a  type  which  is  quite 
certainly  that  described  as  C.  tschudii,  although  it  is  also  quite  certain 
that  it  is  simply  feral  porcellus.  Breeding  experiments  have  been 
carried  on  with  a  fifth  species,  C.  aperea,  by  Nehring  (1894). 

The  C.  rufescens  stock  was  derived  from  3  individuals  received  from 
Mr.  Adolph  Hempel,  of  Campinas,  Brazil,  in  1903.  The  history  of 
this  stock  is  fully  described  by  Detlefsen  (1914).  When  received  by 
the  writer,  most  of  the  stock  consisted  of  hybrids  containing  only  from 
TV  *°  TTT  rufescens  blood.  There  were  a  few  \  and  |  bloods  and  one  f 
blood,  9  A68,  which  is  still  alive  (August  1915)  at  the  remarkable  age  of 
8  years  1  month,1  a  good  illustration  of  the  vigor  of  the  first-generation 
hybrids.  All  of  the  pure  rufescens  stock  has  died  out.  The  rufescens 
hybrids  have  been  crossed  with  nearly  all  of  the  guinea-pig  stocks  to 
be  described,  and  most  of  the  color  varieties  may  be  found  among  them. 
The  ticked-bellied  type  of  agouti  has  been  found  only  among  them  and 
in  pure  rufescens.  C.  rufescens  was  not  completely  fertile  with  the 
guinea-pigs  (Detlefsen,  1914).  Detlefsen  found  that  while  the  female 
hybrids  were  fertile,  all  of  the  male  hybrids  obtained  were  sterile.  In 
the  |  rufescens,  derived  by  crossing  the  females  with  guinea-pigs,  the 
males  were  again  all  sterile.  Not  until  the  |  bloods  were  obtained  did 


October  1915,  aged  8  years,  3  months.  —  W.  E.  C. 
74 


MATERIAL.  75 

a  few  fertile  males  appear.  The  percentage  of  fertile  males  gradually 
increased  in  later  generations. 

The  Cavia  cutleri  stock  was  derived  from  animals  captured  by  Pro- 
fessor Castle  in  Peru  in  191 1 .  Like  C.  rufescens,  these  are  much  smaller 
than  the  guinea-pig.  All  show  the  agouti  pattern.  The  color  is 
described  on  page  59.  Unlike  C.  rufescens,  C.  cutleri  breeds  freely  hi 
captivity  and  crosses  readily  with  the  guinea-pig.  The  male  and 
female  hybrids  are  fertile. 

The  lea  stock  of  guinea-pigs  was  derived  from  3  guinea-pigs  which 
were  obtained  by  Castle  near  lea,  Peru,  in  1911.  They  were  as  large  as 
or  larger  than  average  guinea-pigs,  and  of  a  rich  golden  agouti  color, 
very  different  from  C.  cutleri.  Two  independent  color  variations 
appeared  at  once  in  the  pure  stock,  viz,  black  (aa)  and  red-eye  (CrCr). 
Such  variations  are  very  uncommon  among  wild  species  of  animals; 
e.  g.,  none  has  occurred  within  the  pure  rufescens  or  cutleri  stocks. 
Both  of  these  variations  are  found  in  domesticated  guinea-pigs  in  Peru 
(Arequipa  stock).  From  the  description  of  Cavia  tschudii,  quoted  in 
Waterhouse  (1848)  under  the  name  C.  cutleri  Tschudi,  it  seems  clear 
that  our  lea  stock  is  the  same  as  the  former,  which  was  likewise 
described  from  lea.  In  view,  however,  of  the  size,  color,  and  possession 
of  recessive  color  varieties  found  among  tame  guinea-pigs  of  Peru, 
there  can  be  little  doubt  that  they  are  feral  porcellus. 

The  Arequipa  stock  comes  from  a  pair  of  guinea-pigs  brought  from 
Arequipa,  Peru,  by  Castle  in  1911.  He  obtained  them  from  Indians 
who  had  them  under  domestication.  Owing  to  the  early  death  of  the 
only  female,  no  pure  stock  could  be  developed,  but  numerous  descen- 
dants have  been  derived  from  the  original  male  1002,  a  sepia-cream 
agouti  with  white  and  cream  spots,  demonstrated  to  be  of  constitution 
EEAaBBPpCdCr,  and  from  a  son  of  the  original  pair,  male  1007,  a 
yellow  agouti  with  white  and  yellow  spots,  demonstrated  to  be  of  con- 
stitution EeAaBBPPCjjCd.  These  were  crossed  mainly  with  the  4-toe 
and  BW  stocks,  which  are  described  below.  For  a  full  discussion  of  the 
origin  and  nature  of  the  pure  cutkri,  lea,  and  Arequipa  stocks,  see 
Parti. 

The  Lima  stock  comes  from  8  guinea-pigs  obtained  from  Indians  near 
Lima,  Peru,  by  Professor  Brues  in  1913.  These  guinea-pigs  and  their 
descendants  have  only  recently  been  crossed  with  other  stocks.  There 
have  been  no  agoutis  in  this  stock.  The  pink-eye  and  yellow  variations, 
as  well  as  white  spotting  (but  not  yellow  spotting),  have  occurred  in 
this  stock.  A  pink-eyed  red,  the  lowest  recessive,  of  this  stock  is  of 
constitution  eeaaBBppCC.  There  were  both  rough-furred  and  smooth- 
furred  individuals  in  the  original  stock. 

The  following  stocks  come  from  guinea-pigs  obtained  from  fanciers 
by  Professor  Castle  and  have  been  maintained  for  several  years  at  the 
Bussey  Institution. 


76 


INHERITANCE    IN    GUINEA-PIGS. 


BB  stock. — A  stock  consisting  exclusively  of  very  intense  blacks. 
No  red  or  white  spotting  has  been  observed  among  them.  Unfortu- 
nately it  is  a  stock  of  low  fertility,  and  could  not  be  used  much  to 
advantage. 

BW  stock. — This  stock  has  for  years  consisted  exclusively  of  very 
intense  blacks  and  very  sooty  albinos.  The  blacks  occasionally  show 
a  few  red  hairs  or  a  small  red  patch.  This  has  been  an  extremely 
useful  stock,  among  other  things,  furnishing  albinos  known  to  be  geneti- 
cally identical  with  blacks,  except  for  the  albino  factor.  (Race  B  of 
Parti.) 

Four-toe  stock. — This  is  a  much-inbred  stock,  practically  all  the  indi- 
viduals of  which  show  four  good  toes  on  the  hind  feet  instead  of  the 
normal  three.  This  stock  was  developed  by  selection  and  inbreeding 
by  Professor  Castle  (Castle,  1906).  Most  of  the  individuals  are  a  dull 
black  with  dull  red  blotching  and  brindling  and  often  with  white  spots. 
Albinos  appear  quite  frequently  and  reds  much  more  rarely. 

TABLE  34. — Genetic  formula  of  stocks. 


Stock.     . 

Color. 

Roughness. 

Mendelian. 

Unanalyzed. 

Men- 
delian. 

Unana- 
lyzed. 

Cavia  cutleri  
Cavia  rufescens  .... 
lea  

E      A         B      P      C 
E      A'       B      P      C 
E      A,a     B      P      C,Cr 
E,e  A,a      B      P,p  C,Cd,Cr 
E,e  a          B      P,p  C 
E      a         B      P      C 
E     a          B      P      C,Ca 
E(e)a         B     P      C,Ca 
E      a         B,b  P      C 
E,e  a         B      P      Cd,Ca 
e       a          b       P      Cd,Ca 
E,e  A,A',aB,b  P      C,Cd,Cr,Ca 

2int  — 

r       S 
r       S 
r       S 
R,r  s 
R,r  (S)s 
r       s 
r       s 
R,r  s 
R,r  S,s 

2-    .... 
2-    .... 
....  2R 
....  2R 
2-    .... 
2-    .... 
....  2R 
2+   .... 

(2w2y)  2int  + 
2w2y      2int  + 
2w 

Arequipa  

Lima  

BB  

2int  + 

BW  

(2y)        2int  + 
2wSy      Sint  - 
2wSy      

4-toe  

Tricolor  

Sepia  +  cream  

(2w2y)  2int- 
2int  — 

r       s 
r       s 
R,r  S,s 

Brown-eyed  cream  .  . 
C.  rufescens  hybrids  . 

2w2y      2int± 

In  the  tricolor  stock  the  fur  is  typically  a  patchwork  of  red,  white,  and 
black.  Full-roughs,  partial-roughs,  and  smooths  occur  among  them. 
The  writer  has  used  many  guinea-pigs  of  very  mongrel  ancestry,  which, 
however,  owe  their  partial  rough  coat  to  this  stock. 

The  sepia-and-cream  and  brown-eyed  cream  stocks  have  been  selected 
for  years  for  extreme  dilution.  The  former  stock  consists  exclusively 
of  sepias,  black-eyed  yellows  and  creams,  and  albinos.  The  latter 
consists  exclusively  of  brown-eyed  yellows  and  creams  and  albinos. 
(Race  C  of  Part  I.)  In  the  tables,  these  together  are  called  dilute- 
selection  stock. 

Table  34  shows  the  Mendelian  factors  affecting  color  and  roughness 
of  fur  which  occur  in  each  stock.  Unanalyzed  hereditary  conditions 
which  affect  color  and  roughness  are  also  included,  prefixed  by  the 
symbol  S.  Sw  and  Sy,  as  has  already  been  stated,  mean  hereditary 


INHERITANCE    OF   DILUTION.  77 

white  and  yellow  spotting  respectively.  2  int+  and  2  int—  mean 
hereditary  constitutions  which  intensify  or  dilute,  respectively,  the 
color  associated  with  a  given  array  of  Mendelian  factors.  2  +  and  2  — 
in  the  rough  column  have  a  similar  meaning  with  respect  to  the  rough 
character.  2R  means  the  presence  of  roughness  of  a  different  kind 
from  that  analyzed.  Where  a  factor  occurs  only  rarely  in  a  stock,  it 
is  inclosed  in  parentheses. 

PROBLEMS. 

The  inheritance  of  the  discontinuous  color  variations  which  are  known 
in  guinea-pigs  has  been  solved  by  previous  work.  After  each  factor 
variation  from  the  wild  type  (Cavia  cutleri)  in  the  definitions  of  the 
factors  the  principal  papers  on  the  subject  are  given.  The  writer  has 
been  concerned  mainly  with  an  analysis  of  inheritance  in  the  contin- 
uous series  of  variations  by  which  each  of  the  intense  colors — red, 
brown,  and  black— grade  into  dilute  colors  and  ultimately  white.  A 
second  group  of  problems  concerns  the  variations  in  the  amount  of 
yellow  ticking  in  agoutis.  The  writer  has  worked  with  the  agouti 
patterns  of  Cavia  cutleri,  C.  rufescens  hybrids,  and  tame  guinea-pigs. 
The  inheritance  of  variations  in  the  rough  coat  occasionally  found  in 
guinea-pigs  is  discussed  in  a  later  section. 

INHERITANCE  OF  DILUTION. 

THE  RED-EYE  FACTOR. 

The  experiments  with  dilution  have  become  closely  associated  with 
experiments  with  certain  imported  South  American  stocks  (lea,  Are- 
quipa)  which  are  discussed  in  detail  in  Part  I.  A  number  of  hitherto 
unknown  color  varieties  appeared  in  these  stocks,  the  inheritance  of 
which  could  be  explained  by  assuming  the  existence  of  a  new  allelo- 
morph of  albinism  intermediate  in  effect  and  dominance  between  albin- 
ism and  its  normal  allelomorph.  More  specifically,  this  new  factor 
is  characterized  by  the  production  of  red  eyes,  slight  dilution  of  black 
in  the  fur,  and  complete  inhibition  of  yellow  pigment  development. 

The  writer  has  used  animals  of  both  the  lea  and  Arequipa  stocks  in 
experiments,  with  results  in  full  agreement  with  those  given  in  Part  I. 
Crosses  20-1  and  21  to  25  involve  red-eye  (from  lea  stock)  without 
also  involving  dilution.  In  cross  20-1  a  pure  lea  male,  a  red-eyed 
agouti,  is  crossed  with  intense  guinea-pigs,  giving  young  all  intense. 
This  illustrates  the  dominance  of  intensity  over  red-eye. 

In  cross  21  a  pure  lea  intense  male  crossed  with  albinos  of  intense 
stock  gives  both  intense  and  red-eye  young.  The  lea  male  no  doubt 
was  heterozygous  for  red-eye,  but  the  albinos  could  not  possibly  trans- 
mit red-eye,  as  they  come  from  a  stock  hi  which  red-eye  has  never 
appeared.  This  illustrates  the  apparent  reversal  of  dominance  of  red- 
eye whenever  albinism  is  introduced  into  a  cross.  A  further  illus- 
tration is  given  in  cross  23,  in  which  red-eye  by  albino  of  intense 


78  INHERITANCE    IN   GUINEA-PIGS. 

stock  gives  red-eyes,  but  no  intense  young.  In  cross  25,  red-eyes 
crossed  with  albinos  from  various  sources  give  no  intense  young,  but 
only  red-eyes  and  albinos.  One  possible  explanation  of  these  results 
would  be  the  supposition  that  red-eye  becomes  dominant  over  its 
normal  allelomorph  in  the  presence  of  heterozygous  albinism.  In 
this  case  intense  young  should  appear  when  such  heterozygous  red-eyes 
are  crossed  together;  but,  as  is  shown  in  cross  24,  none  such  appears. 
Here  red-eyes  from  cross  21,  mated  inter  se,  gave  17  red-eyes,  6  albinos, 
no  intense.  Numerous  results  of  this  kind  have  made  it  clear  that 
intensity  can  never  be  recovered  in  any  generation  after  a  cross  of  red- 
eye with  albino.  This  means  that  neither  red-eye  nor  albino  can  trans- 
mit the  normal  allelomorph  of  the  other.  Now,  the  one  thing  which  a 
recessive  variation,  of  necessity,  can  not  transmit,  is  its  own  normal 
allelomorph.  Therefore  the  normal  allelomorphs  of  red-eye  and  albino 
must  be  identical. 

This  does  not  yet  demonstrate  that  albinism,  red-eye,  and  intensity 
form  a  series  of  three  allelomorphs.  There  is  still  the  possibility  that 
red-eye  and  albinism  involve  the  same  recessive  allelomorph  (Ca)  of 
normal  color  (C),  but  differ  by  an  independent  modifying  factor. 
Symbolically  we  could  suppose  albinos  to  be  CaCarr,  red-eyes  to  be 
CaCaRR  (or  CaCaRr),  intense  guinea-pigs  of  ordinary  stocks  to  be  CCrr 
(or  CCarr) ,  and  intense  guinea-pigs  of  lea  stock  to  be  CCRR  (or  CCaRR) . 
We  must  suppose  the  lea  stock  to  be  homozygous  for  the  modifier  R, 
to  account  for  the  absence  of  albinos.  R  must  be  a  unit  factor  to 
account  for  the  simple  3  to  1  ratio  in  cross  24.  This  hypothesis  fits  all  of 
the  facts  given  so  far.  The  critical  test  of  its  truth  is  the  possibility  (as 
it  turns  out,  impossibility)  of  producing  intense  animals  (CCaRr)  which 
will  give  both  red-eyes  and  albinos  when  crossed  with  albinos.  If 
intensity,  red-eye,  and  albinism  are  triple  allelomorphs,  it  should  be 
impossible  to  obtain  such  animals.  Crosses  21  and  22  are  interesting 
as  furnishing  just  this  test.  Cross  21  may  be  represented  symbolically 
as  follows,  according  to  the  two  hypotheses: 

Albino  (BW)  X  intense  (lea)  =  9  intense  +  4  red-eye. 

(1)  CaCarr       X  CCaRR  =  CCaRr     CaCaRr. 

(2)  CaCa          X  CCr  =  CCa          CrCa. 

In  either  case  the  Fj.  red-eyes  crossed  inter  se  should  give  3  red-eyes 
to  1  albino.  The  result  obtained  in  cross  24  (17  red-eyes  to  6  albinos) 
is  in  nearly  perfect  agreement.  But  the  cross  of  F!  intense  with  albinos 
gives  very  different  results  under  the  two  hypotheses  (cross  22) : 

Albino  X  intense  (Fi)   =  16  intense  +  (0  red-eye)    +  25  albinos. 

(1)  CaCarr  X  CCaRr     =  CCaRr  +  CCair  +  CaCaRr    +  CaCarr. 

(2)  CaCa   X  CCa       =  CCa  +  CaCa- 

The  complete  absence  of  red-eyes  among  the  41  young,  as  well  as  the 
excess  of  albinos  where  an  excess  of  intense  is  expected,  thoroughly 
eliminates  the  first  hypothesis.  The  results  agree  reasonably  well  with 


INHERITANCE   OF   DILUTION.  79 

the  hypothesis  of  triple  allelomorphs,  which  we  have  found  to  agree 
with  the  results  of  all  the  other  crosses.  The  only  possibility  which 
has  not  been  eliminated  is  a  linkage  so  close  as  to  simulate  a  system  of 
triple  allelomorphs.  Unless  exceptions  occur  which  require  it,  such  an 
hypothesis  need  not  be  considered. 

Thus  the  data  obtained  by  the  writer  are  not  only  in  harmony  with 
the  theory  that  albinism,  red-eye,  and  intensity  form  a  series  of  triple 
allelomorphs,  but  can  be  explained  on  no  other  basis,  barring  the  pos- 
sibility just  noted. 

DILUTION. 

Such  color  varieties  as  agouti,  black,  brown,  yellow,  etc.,  are  sharply 
distinct  from  each  other.  They  segregate  from  crosses  without  pro- 
ducing intergrades  and  in  unforced  agreement  with  Mendelian  expec- 
tation. In  contrast  with  these  discontinuous  variations  are  the  con- 
tinuous variations  in  the  intensity  of  color  of  each  main  color  variety. 
Thus,  among  the  yellows,  there  are  all  gradations  from  a  pale  cream  to  an 
intense  red.  Among  the  agoutis,  there  are  the  pale  silver  agoutis,  the 
intense  golden  agoutis,  and  the  intermediate  yellow  agoutis.  There 
are  all  grades  of  dilute  blacks  known  to  the  fanciers  as  blues,  for  which 
term,  as  has  been  explained,  sepia  is  substituted  in  this  paper.  Finally, 
there  are  all  grades  of  dilute  browns  and  cinnamons.  (See  plates  1 
and  2.) 

The  existence  of  these  dilute  types  was  noted  by  Castle  (1905)  and 
Sollas  (1909),  both  of  whom  also  recognized  that  dilution  could  be 
transferred  from  one  series  to  another,  e.  g.,  from  creams  to  blacks, 
giving  rise  to  sepias.  They  did  not,  however,  suggest  any  factorial 
explanation,  finding  the  results  of  crosses  highly  irregular.  Detlefsen 
(1914)  considered  dilution  to  be  recessive,  but  found  the  inheritance  of 
dilution  very  irregular  among  C.  rufescens  hybrids.  He  obtained 
dilutes  in  F!  after  crossing  dilute  hybrids  with  a  race  of  guinea-pigs 
(brindle  or  4-toe),  among  which  dilution  had  never  occurred  and  which 
therefore  should  not  carry  it  as  a  recessive.  It  may  be  remarked  hi 
passing  that  the  4-toe  race  does  contain  albinism,  which,  with  present 
knowledge,  satisfactorily  accounts  for  these  F!  dilutes. 

Thus  the  difficulties  in  the  way  of  an  understanding  of  the  heredity  of 
dilution  have  been  due  (1)  to  the  intergrading  of  dilute  with  intense; 
(2)  to  data  which  seemed  to  indicate  that  dilution  could  be  due  neither 
to  a  recessive  nor  to  a  dominant  unit  factor,  without  complications. 
Cross  39  gives  many  examples  in  which  intense  by  intense  has  given 
very  dilute  young,  which  seems  to  indicate  that  dilution  must  be 
recessive  if  simple  Mendelian  at  all.  On  the  other  hand,  such  cases 
as  that  given  by  Detlefsen  are  difficult  to  interpret  on  this  basis. 
Further,  dilute  by  dilute  has  often  given  young  much  more  intense 
than  either  parent.  Thus,  in  cross  42-8,  we  have  two  medium  sepias 
producing  a  black.  In  cross  37  are  many  cases  in  which  cream  by  cream 


80  INHERITANCE   IN   GUINEA-PIGS. 

has  produced  yellow.  Apparently  intense  by  intense  may  give  any 
intensity  whatever,  and  almost  the  same  can  be  said  of  dilute  by  dilute. 
Amid  this  confusion,  however,  one  cross  has  been  found  which  con- 
sistently gives  a  very  definite,  although  unexpected,  result.  It  is 
found  that  a  dilute  crossed  with  an  albino,  even  of  intense  stock,  never 
gives  intense  young,  but  only  well-defined  dilutes  and  albinos.  There 
are  only  a  few  possible  ways  in  which  this  result  can  be  explained  and, 
from  the  results  of  other  crosses,  all  but  one  of  these  explanations  have 
been  definitely  eliminated,  namely,  that  dilution  is  an  allelomorph  of 
albinism.  An  allelomorph  of  albinism  was  already  known  to  be  respon- 
sible for  the  red-eyed  condition  in  certain  South  American  stocks 
(Castle,  1914a) .  It  could  now  be  shown  that  albinism,  red-eye,  dilution, 
and  intensity  are  due  to  a  series  of  four  allelomorphs  with  dominance 
in  the  order  of  increasing  pigmentation.  A  preliminary  account  of  this 
demonstration  has  been  given  in  a  previous  paper  (Wright,  1915).  In 
the  present  paper  the  demonstration  is  given  in  more  detail  and  further 
steps  are  taken  in  the  analysis  of  the  variations. 

THE  DILUTION  FACTOR. 

The  dilute  varieties  have  some  resemblance  to  the  red-eyed  varieties. 
The  fact  that  red-eye  is  due  to  an  allelomorph  of  albinism  suggested 
that  dilution  might  also  be  due  to  a  member  of  the  same  series  of  alle- 
lomorphs. A  stock  was  chosen  which  was  known  to  carry  no  dilution. 
This  was  the  BW  stock,  which  for  years  has  consisted  exclusively  of  the 
most  intense  blacks  and  sooty  albinos.  The  following  crosses  were 
designed  to  eliminate  the  hypothesis  of  allelomorphism  if  incorrect : 

(1)  Albinos  from  intense  stock  were  crossed  with  dilutes: 

CaCall  X  CCii  =  CCali. 

(2)  Albinos  from  dilute  stock  were  crossed  with  blacks  of  intense  stock : 

CaCaii  X  CCII   =  CCaIi. 

If  intensity  and  dilution  form  a  pair  of  allelomorphs  (I,  i)  which 
segregate  independently  of  the  pair  color  and  albinism  (C,  CJ,  as  is  the 
case  in  mice  and  rabbits,  these  two  crosses  must  give  identical  results. 
In  each  case,  color  is  introduced  by  one  parent,  albinism  by  the  other; 
intensity  by  one  parent,  dilution  by  the  other.  In  fact,  identical  results 
should  be  obtained  regardless  of  whether  dilution  is  due  to  a  unit  factor 
or  to  multiple  factors,  or  even  whether  its  inheritance  is  Mendelian  or 
not,  provided  only  that  it  is  inherited  independently  of  albinism. 
Crosses  16  and  17  and  table  35  give  the  actual  results.  All  cases  are 
included,  which  involve  an  intense  stock  known  to  carry  no  dilution. 

Among  those  called  dilute  below  (among  the  young),  none  was  more 
intense  than  sepia2  or  yellow4.  Among  the  intense,  none  was  more 
dilute  than  a  dull  black  comparable  in  grade  but  not  in  color  with  sepia2, 
or  a  red  in  very  few  if  any  cases  as  dilute  as  yellow2.  There  was  there- 
fore no  difficulty  in  drawing  a  natural  line  between  intense  and  dilute 
in  these  crosses. 


INHERITANCE    OF   DILUTION. 


81 


It  is  evident  that  the  two  sets  of  crosses  give  consistently  different 
results.  This  difference  demonstrates  that  dilution  does  not  segregate 
independently  of  albinism. 

An  even  more  striking  result  follows  from  a  portion  of  the  above  data. 
Fj  dilutes,  one  of  whose  parents  was  of  intense  stock,  were  back-crossed 
with  albinos  of  intense  stock.  They  gave  9  dilute,  20  albino  young, 
no  intense,  although  these  young  were  at  least  three-quarters  of  intense 
stock.  On  the  other  hand,  Fi  intense,  one  of  whose  parents  was  an 
albino  of  dilute  stock,  were  back-crossed  with  albinos  of  dilute  stock. 
They  gave  5  intense,  7  albinos,  no  dilutes,  although  these  young  were 
at  least  three-quarters  of  dilute  stock.  It  is  clear  that  the  hereditary 
difference  between  a  dilute  and  an  intense  can  not  be  transmitted 
through  an  albino. 

TABLE  35. 


Intense. 

Dilute. 

Red-eyed. 

White. 

cf  albino  (intense  stock)  X  9  dilute  

56 

5 

39 

9  albino  (intense  stock)  X  cf  dilute  

29 

10 

21 

Total  

85 

15 

60 

d*  albino  (dilute  stock)  X  9  intense  (intense  stock)  .  . 
9  albino  (dilute  stock)  X  c?1  in  tense  (intense  stock)  .  . 

47 
9 

10 
2 

56 

12 

It  was  emphasized  above  that  all  the  intense  animals  used  in  cross  17 
came  from  stocks  which  have  never  given  dilutes.  This  was  necessary 
because  in  other  crosses  (18,  34,  41)  intense  by  albino  has  given  many 
dilute  young.  No  such  precaution  was  taken  with  the  dilutes  used  in 
cross  16.  Any  available  dilutes  were  used  regardless  of  ancestry.  In 
fact,  1 1  of  them,  with  38  young,  had  one  or  both  parents  intense.  In 
none  of  the  other  crosses  in  which  dilute  has  been  crossed  with  albino 
(19,  27,  38,  44)  has  any  intense  young  appeared.  Thus  in  crosses 
with  albinos  an  intense  may  transmit  dilution,  but  a  dilute  never  trans- 
mits intensity.  From  these  crosses  it  seems  clear  that  intensity  is  dom- 
inant over  dilution.  Other  crosses  on  the  whole  bear  this  out.  The 
apparent  exceptions  will  be  ignored  for  the  present  but  discussed  later. 

We  have  reached  the  definite  conclusion  that  dilute  by  albino  can 
never  give  intense,  regardless  of  ancestry  on  either  side.  Since  the 
only  thing  which  a  variety  of  necessity  can  not  transmit  is  a  dominant 
allelomorph  of  its  essential  factor,  it  follows  that  dilution  and  albinism 
must  have  the  same  dominant  allelomorph,  which  we  will  call  intensity. 

There  are  only  a  few  hypotheses  which  will  satisfy  this  condition. 
We  already  know  two  recessive  allelomorphs  of  intensity,  viz,  red-eye 
and  albinism.  It  is  conceivable  that  dilution  may  be  due  to  the 
cooperation  of  an  independent  factor  (or  factors)  with  one  or  more  of 
the  known  combinations  CrCr,  CrCa,  and  CaCa.  If  this  is  not  the  case, 


82  INHERITANCE   IN   GUINEA-PIGS. 

dilution  must  be  due  to  a  new  allelomorph  in  the  albino  series,  let  us 
say  Cd-  A  modifying  factor  which  shows  partial  coupling  would  give 
intermediate  results. 

(1)  Since  dilution  and  red-eye  show  considerable  resemblance,  it 
would  be  a  plausible  hypothesis  to  assume  that  they  are  due  to  the  same 
allelomorph  in  the  albino  series  (Cr)  but  differ  by  an  independent  modi- 
fying factor  (D).    With  this  hypothesis,  all  stocks  used  (except  the  lea 
and  Arequipa)  must  needs  be  homozygous  for  the  modifier  in  order 
that  no  red-eyes  should  appear.     Dilutes  would  be  CrCrDD  or  CrCaDD 
albinos  CaCaDD  in  these  stocks.    Thus  albinos  of  these  stocks  should 
transmit  the  modifier  and  in  crosses  with  red-eyes  (CrCrdd)  should 
produce  dilutes  at  least  in  F2.    But  in  crosses  23  and  25,  red-eyes  mated 
with  such  albinos  have  given  no  dilutes,  nor  have  dilutes  appeared  in 
F2  in  cross  24,  among  23  young.     Thus  an  albino  can  not  transmit  the 
hereditary  difference  between  a  dilute  and  a  red-eye  and  the  hypothesis 
is  untenable. 

(2)  Next  to  be  considered  is  the  hypothesis  that  there  is  a  modifier 
which  converts  into  a  dilute  an  annual  which  would  otherwise  be  an 
albino.    Dilutes  of  ordinary  stock  would  be  CaCaDD  or  CaCaDd.     In 
cross  20,  dilutes  of  ordinary  stock  crossed  with  a  pure  lea  male  No. 
724,  a  homozygous  red-eye  (CrCrdd),  produced  5  dilute  young  which 
must  be  of  formula  CrCaDd.    This  shows  that  if  the  hypothesis  is  to 
stand  at  all,  it  must  be  extended,  so  that  the  factor  which  converts  an 
albino  into  a  dilute  also  converts  a  red-eye  into  a  dilute.    The  fact 
that  a  dilute  may  transmit  red-eye  (crosses  19  and  27)  is  further  evi- 
dence that  this  extension  is  necessary.     In  this  form  most  of  the  results 
can  be  explained  satisfactorily. 

(3)  The  only  other  hypothesis  which  remains  is  that  dilution  is  due 
to  a  new  allelomorph  in  the  albino  series  making  a  series  of  four — C, 
Cd,  Cr,  and  Ca.    The  results  cited  above  (crosses  20,  19,  and  27)  make 
it  evident  that  dilution  is  dominant  over  red-eye.    The  meaning  of  a 
series  of  four  allelomorphs  can  be  made  clear  by  considering  all  of  the 
possible  zygotic  formulae.    Every  zygote  must  have  two  representatives 
from  the  series,  but  never  more  than  two.     Intense  guinea-pigs  may  be 
homozygous  (CC),  or  carry  dilution  (CCd),  or  red-eye  (CCr),  or  albin- 
ism (CCa),  but  can  never  transmit  more  than  one  of  the  recessive 
conditions.     Dilutes  may  be  homozygous  (CdCd)   or  carry  red-eye 
(CdCr)  or  albinism  (CdCJ,  never  both.    Red-eyes  may  be  homozygous 
(CrCr)  or  carry  albinism  (CrCa),  while  albinos  can  only  be  homozygous 
(CaCa)  and  can  never  transmit  any  of  the  higher  conditions. 

The  critical  test  between  this  hypothesis  of  four  allelomorphs  and  the 
preceding  one  (that  dilute  is  a  modified  red-eye  or  albino),  lies  in  the 
possibility  or  impossibility  of  producing  animals  which  in  crosses  with 
albinos  will  transmit  more  than  one  recessive  condition."  If  an  intense 
animal  can  be  obtained  which  transmits  both  dilution  and  red-eye 


INHERITANCE    OF   DILUTION.  83 

(CCrDd)  or  dilution  and  albinism  (CCaDd),  or  if  a  dilute  can  be  obtained 
which  transmits  both  red-eye  and  albinism  (CrCaDd),  the  hypothesis 
of  modifiers  must  be  adopted.  But  all  attempts  to  obtain  these  double 
heterozygotes  have  failed.  All  of  the  results  substantiate  the  hypothesis 
of  quadruple  allelomorphs. 

Arequipa  male  No.  1007  was  of  formula  CrCrDD  or  CdCd,  depending 
on  the  hypothesis  chosen  (see  crosses  28  to  34).  He  was  crossed  with 
intense  guinea-pigs  of  BW  or  4-toe  stock,  known  to  transmit  no  dilu- 
tion (CCadd  or  CCa) .  The  intense  young  could  only  be  CCrDd  or  CCd 
under  the  two  hypotheses.  Five  of  them  were  crossed  with  albinos  and 
gave  13  intense,  20  dilute  young,  no  others  (cross  34).  Expectation 
on  the  hypothesis  of  a  moolifier  is  16  intense,  8  dilute,  8  red-eye.  On 
the  hypothesis  of  allelomorphs  it  is  16  intense  to  16  dilute.  Both  the 
excess  of  dilutes  and  the  absence  of  red-eyes  point  conclusively  to  the 
latter. 

In  cross  18,  intense  guinea-pigs,  each  of  which  had  a  dilute  parent 
known  to  transmit  albinism  and  with  no  lea  or  Arequipa  blood,  are 
crossed  with  albinos  or  red-eyes.  Under  the  modifier  hypothesis  we 
would  expect  about  half  of  them  to  be  CCaDd.  Under  the  allelomorph 
hypothesis,  they  should  be  CCa  or  CCa.  As  it  turned  out,  there  were  6 
which  gave  only  intense  and  dilute  (30  intense,  35  dilute)  and  8  which 
gave  no  dilute  young  (57  intense  to  61  red-eye  or  albino).  Thus  there 
was  no  intense  which  had  dilute  young  and  also  red-eyes  or  albinos. 
This  result  distinctly  favors  the  hypothesis  of  allelomorphs. 

In  crosses  19  and  27  dilutes,  each  from  the  cross  of  a  red-eye  with  a 
stock  guinea-pig  free  from  South  American  ancestry,  are  crossed  with 
albinos.  Under  the  modifier  hypothesis,  those  which  transmit  red-eye 
at  all  are  necessarily  CrCaDd,  for  they  must  be  CraCraD  in  order  to 
appear  dilute;  they  could  get  Ca,  but  not  Cr,  from  the  stock  guinea-pig 
parent,  and  they  would  necessarily  get  d  from  the  red-eye  parent. 
Under  the  allelomorph  hypothesis,  they  should  be  CdCr,  the  rest  CaCa; 
9  gave  only  dilutes  and  red-eyes  (18  dilutes,  24  red-eyes);  9  others 
gave  only  dilutes  and  albinos  (20  dilutes,  16  albinos).  There  were  3 
which  had  had  only  8  dilute  young  when  tabulated.  The  fact  that 
none  of  the  9  which  had  red-eye  young  also  had  albinos  among  42 
young  gives  a  third  body  of  evidence  pointing  toward  the  allelomorph 
hypothesis. 

These  results  make  it  reasonably  certain  that  the  allelomorph  hypo- 
thesis is  correct.  The  only  other  possibility  would  involve  coupling  so 
close  as  to  simulate  multiple  allelomorphs.  The  hypothesis  of  allelo- 
morphs has  been  reached  by  a  method  of  elimination.  It  remains  to 
show  that  all  of  the  data  are  in  harmony  with  it.  In  the  next  section, 
definite  conclusions  are  reached  as  to  the  inheritance  of  variations  in 
intensity  and  dilution  which  make  it  possible  to  distinguish  intense 
animals  from  dilute  in  all  but  very  exceptional  cases. 


84 


INHERITANCE   IN    GUINEA-PIGS. 


The  following  table  gives  a  summary  of  the  data  bearing  on  the 
inheritance  of  the  albino  series  of  allelomorphs  based  on  these  conclu- 
sions. It  will  be  noticed  that  animals  of  every  possible  formula  have 
been  tested  by  crosses  with  albinos,  the  lowest  recessives.  No  attempt 
has  been  made  to  make  all  other  possible  crosses,  and  several  (especially 

TABLE  36. — Summary  of  albino  series  crosses  (crosses  16  to  44)- 


Parents. 

Formulae. 

Int. 

Dil. 

R.E. 

W. 

From  crosses  — 

Intense  X  albino      .      .  . 

CC      X  CaCa 

40 

17a  6. 

31 

36 

186,  34,  41 

9 

4 

21 

64 

71 

17c,  17d,  18c,  22 

Dilute  X  albino  

CdCdX  CaCa... 

26 

16a,  38a,  44 

18 

24 

19,27 

Red-eye  X  albino  

CdCa       CaCa-  •  • 

98 

30 

79 

166,  16c,  19,  27,  33,  386,  44 
25 

6 

3 

23,  25 

Albino  X  albino   

x 

Long  established. 

Intense  X  red-eve   

cc    x(£r£rl.. 

9 

20 

ICrCaJ 

ccd    /SrSrV- 

28 

31 

18a,  20 

Dilute  X  red-eye  

(.C-r^aJ 

cc-    & 

CdCdx(£r£rV. 

25 

15 

20 

7 

18c 
20  26  43 

|_UrOaJ 

1 

1 

20 

13 

5 

g 

26  43 

Red-eye  X  red-eye  

17 

6 

24 

Intense  X  dilute  

CC     X  CdCd.  . 

14 

28 

CC           CdCa.  . 
CCd        CdCd  .  . 

12 

in 

7 

35 

29,  40o 

CCd         CdCa.  .  • 

39! 

40 

32,  36,  40a 

CCa         CdCd  -  . 

191 

10 

28,  40o 

Dilute  X  dilute  .   ....... 

C/C_/a         ^d^-'a-  •  • 
CdCdX  CdCa... 

28 

22 
15 

15 

36,  406 
30  37  42 

Intense  X  intense  

CdCa       CdCa-  •  • 
CCd   X  CCd  .  .  • 

57 

82 
19 

24 

37,42 
31  39 

CCd        CCa.  -  -  • 

75 

35 

39 

CC          CC  

x 

See  rough  and  Lima  crosses. 

ones  involving  red-eye)  have  not  yet  been  made  by  the  writer.  The 
last  column  refers  to  the  crosses  tabulated  at  the  end  of  the  paper. 
The  ratios  expected  are  obvious  from  the  nature  of  the  matings,  except 
that  39  to  44  were  not  random  crosses  of  their  kind.  The  appearance 
of  recessive  young  was  used  as  a  criterion  of  the  nature  of  the  parents 
in  these  cases.  This  causes  an  excess  of  recessives  to  be  expected. 


INHERITANCE    OF   MINOR   VARIATIONS   IN   INTENSITY.          85 

INHERITANCE  OF  MINOR  VARIATIONS  IN  INTENSITY. 

METHODS  AND  ACCURACY  OF  GRADING. 

The  method  of  grading  has  been  described  on  page  60.  Every 
guinea-pig  which  showed  dilute  black  or  yellow  in  the  fur  was  compared 
with  standard  samples  of  hair  within  a  week  of  birth.  These  samples 
were  black0,  sepia3,  sepiag,  and  sepiag,  in  the  black  series,  and  red0, 
yellow3,  and  creams  in  the  yellow  series.  Intermediate  grades  were 
given  by  estimate.  Grades  were  taken  later  in  life  in  many  cases  hi 
order  to  determine  the  relation  of  age  to  intensity  of  pigmentation. 

In  interpreting  the  results,  it  is  important  to  know  the  accuracy  with 
which  the  grading  could  be  done  and  the  difficulties  met.  In  some 
cases  the  back  and  belly  are  f airly  uniform  in  intensity,  but  usually  the 
belly  is  considerably  the  lighter.  Tufts  of  hair  for  grading  have  always 
been  taken  as  near  the  middle  of  the  back  as  possible. 

In  some  cases  the  hair  is  of  fairly  uniform  intensity  from  base  to  tip. 
In  most  cases,  however,  the  base  is  very  much  lighter  than  the  tip. 
The  color  at  the  tip  has  been  used  in  grading,  although  extreme  varia- 
tions in  the  intensity  at  the  base  have  also  been  noted.  The  color  at 
the  tip  has  most  to  do  with  the  general  appearance  of  the  animal. 

The  attempt  has  been  made  to  get  both  a  yellow  and  a  sepia  grade  for 
every  animal,  so  that  the  correlation  between  the  intensities  in  these 
series  could  be  determined.  This  is  easy  in  the  sepia  and  yellow-spotted 
animals,  but  in  agoutis  (where  the  yellow  band  of  the  agouti  pattern 
displaces  the  sepia  near  the  tip  of  the  hair)  determination  of  the  inten- 
sity of  sepia  has  not  been  so  satisfactory.  Several  independent  determi- 
nations have  been  taken  in  many  of  these  cases.  In  most  cases  the 
same  grade  was  assigned  the  second  time  and  rarely  did  the  second 
grade  differ  from  the  first  by  more  than  one  point. 

VARIATIONS  IN  INTENSE  GUINEA-PIGS  AND  ALBINOS. 

Before  discussing  the  inheritance  of  variations  among  dilutes,  it  will 
be  well  to  note  briefly  the  range  of  variation  among  guinea-pigs  which 
have  the  intensity  factors  (CP).  In  the  BW  race  the  blacks  are  a  very 
intense  black.  The  base  of  the  hair  is  only  slightly  lighter  than  the 
tip.  In  other  races,  especially  the  4-toe  stock,  the  tip  of  the  hair  is  a 
dull  slaty  black  and  the  base  a  very  dull  color,  often  with  less  pigment 
than  many  typical  dilutes.  The  animals  have  a  dull  streaky  black 
appearance  very  different  usually  from  the  uniform  dark  sepia  of  the 
darker  dilutes.  This  dull  color  is  not  associated  with  heterozygous 
albinism.  Male  M330  was  undoubtedly  homozygous  (CC),  having 
had  9  intense  young  by  albino  females  and  no  others;  yet  he  was  one 
of  the  dullest  blacks  in  stock.  On  the  other  hand,  nearly  all  of  the 
intense  blacks  of  the  BW  race  are  heterozygous  for  albinism. 


86  INHERITANCE    IN   GUINEA-PIGS. 

This  dull  black  can  not  be  due  to  an  allelomorph  of  albinism  between 
intensity  (C)  and  dilution  (Cd),  since  it  is  a  condition  which  can  be 
transmitted  by  albinos.  Indeed,  the  albinos  themselves  of  the  BW 
and  4-toe  stocks  differ  conspicuously  in  appearance.  The  BW  albinos 
have  jet  black  ears  and  feet,  dark  smudges  on-  the  nose,  and  usually 
some  sootiness  on  the  back.  The  4-toe  and  most  other  albinos  (at  the 
Bussey  Institution)  have  very  much  less  black  on  ears,  nose,  and  feet, 
and  the  rest  of  the  fur  is  pure  white. 

There  are  parallel  variations  hi  the  intensity  of  red  in  these  stocks. 
The  occasional  red  spots  in  the  BW  race  are  of  a  very  intense  red 
(standard  redo).  In  the  4-toe  and  other  dull  stocks  the  red  is  consider- 
ably less  intense,  especially  at  the  base  of  the  hair.  The  most  dilute 
grade  found  hi  tame  guinea-pigs  known  to  have  factor  C  is  yellow2 
(D12  cross  35-1). 

The  wild  Cavia  cutleri  is  quite  light  in  color.  The  black  of  the  fur 
is  a  dull  slaty  color,  more  like  the  dull  black  of  the  4-toes  than  any  other 
color  in  tame  guinea-pigs.  The  yellow  on  the  back  is  about  yellow3, 
on  the  belly  creams.  In  spite  of  the  resemblance  to  tame  yellow 
agoutis,  Cavia  cutleri  has  the  intensity  and  not  the  dilution  factor. 
When  crossed  with  animals  of  the  BW  race,  whether  blacks  or  albinos, 
the  young  are  intermediate  in  intensity  and  would  be  called  intense 
(Parti).  Crossed  with  black  animals  of  the  4-toe  race,  the  young 
are  but  little  more  intense  than  Cavia  cutleri.  (See  plate  3.) 

Summing  up :  All  variations  maybe  found  among  intense  guinea-pigs, 
from  uniform  black0  to  a  dull  slaty  black2  and  from  red0  to  yellow2.  In 
the  dull  grades  the  hair  is  especially  dull  at  the  base.  These  variations 
are  hereditary,  but  have  not  been  analyzed.  The  hereditary  factors 
for  these  variations  in  intense  guinea-pigs  are  responsible  for  visible 
differences  among  albinos.  It  is  to  be  expected,  as  indeed  is  the  case, 
that  variations  will  be  found  among  dilutes,  for  which  these  same 
unanalyzed  hereditary  differences  of  different  stocks  are  responsible. 
Finally,  the  residual  heredity  of  all  tame  guinea-pigs  has  more  intensi- 
fying effect  than  that  of  Cavia  cutleri,  the  wild  species. 

MULTIPLE  ALLELOMORPHS. 

The  presence  of  at  least  four  allelomorphs  in  the  albino  series  suggests 
the  hypothesis  that  other  allelomorphs  in  the  series  may  be  responsible 
for  the  intermediate  grades  hi  intensity.  It  is  a  tempting  hypothesis 
to  suppose  that  the  continuous  series  of  variations  is  correlated  with  a 
continuous  series  of  allelomorphs,  such  that  each  grade  of  intensity  is 
dominant  over  all  lower  grades.  If  this  were  the  case  a  stock  of 
dilutes,  hi  which  all  derive  their  dilution  from  a  single  gamete  of  one 
animal,  should  be  fairly  constant  hi  their  degree  of  dilution.  Again,  the 
cross  of  dilute  by  dilute  should  never  give  young  more  intense  than  the 
darker  parent. 


INHERITANCE   OF   MINOR   VARIATIONS  IN   INTENSITY.          87 

However,  both  of  these  tests  fail.  No  single  gamete  stock  of  dilutes 
has  been  found  which  will  not  give  the  entire  range  of  variation  when 
tested.  Thus,  male  D30  redo,  an  intense  which  carried  dilution  as  a 
recessive  (CCd),  was  crossed  with  red-eyes.  His  dilute  young  must  all 
owe  their  dilution  to  the  same  single  gamete.  They  ranged  from  D340 
blacki  to  D 152  sepia5.  Yellows  which  owe  their  dilution  to  this  same 
single  gamete  (derived  from  male  00  creame  CaCa,  the  father  of  D30) 
range  from  D391  yellow2  to  00  creamy .  Dilution  from  a  single  gamete 
of  A674  sepiae  (CdCa)  has  given  rise  to  D652  black!  and  M306  sepia?, 
D409  yellow3,  and  M199  cream7.  This  last  case  involves  no  admixture 
of  South  American  blood.  Inspection  of  the  tables  will  yield  many 
similar  cases.  Evidently  dilution  from  a  single  gamete  may  appear  hi 
dilutes  of  any  grade  of  intensity.  The  extreme  variations  may  occur 
within  a  single  litter  (offspring  of  D30).  Again,  many  examples  can  be 
given  in  which  the  offspring  are  much  darker  than  either  parent.  D652 
blacki  was  the  offspring  of  D215  sepia3  and  D106  sepia4.  In  cross  37 
there  are  6  cases  in  which  creame  X  cream^  has  produced  yellow3,  with 
other  less  extreme  cases  of  this  kind.  These  results  do  not  demonstrate 
that  no  more  than  four  allelomorphs  in  the  albino  series  are  present  in 
our  stock.  They  do  show  that  there  are  other  causes  producing  varia- 
tion of  much  more  importance  than  any  other  allelomorphs  which  may 
be  present. 

THE  RELATIONS  OF  IMPERFECT  DOMINANCE,  STOCK,  AND  AGE  TO 
GRADES  OF  INTENSITY. 

In  tables  37  and  38,  and  diagrammatically  in  figure  5  and  figure  6,  all 
records  of  grades  of  dilution  at  birth  are  analyzed  with  respect  to 
genetic  constitution  and  stock.  All  of  those  whose  genetic  constitu- 
tion was  known  with  complete  or  nearly  complete  certainty,  either  from 
parentage  or  from  offspring,  are  put  after  the  proper  formula,  CdCd, 
CaCr,  etc.  All  from  litters  containing  two  classes  are  listed  separately 
with  the  numerical  expectation  of  the  classes  as  (20  CdCd :  32  CdCa),  etc. 
Those  hi  the  litters  whose  formulae  were  later  determined  by  a  test 
mating  are  given  below  in  parentheses.  These  tested  individuals  are 
included  both  among  those  of  certain  constitution  and  hi  the  litters 
containing  two  classes.  No  very  close  analysis  of  the  influence  of 
stock  was  possible  from  the  data  obtained.  However,  the  following 
stocks  were  recognized: 

Dil.,  Dilute  selection  stock. 

Misc.,  Miscellaneous  stocks  with  but  little  BW  blood  and  no  lea  or  Arequipa  blood. 

These  contained  much  dilute  selection  and  4-toe  blood  and  some  C. 

rufescens  ancestry. 

$BW,  FI  from  the  cross  of  miscellaneous  with  BW  stock, 
f BW,  Back-cross  of  $BW  with  BW  stock. 
S.  Am.,  All  animals  with  lea  or  Arequipa  blood,  in  most  cases  about  J  South 

American,  J  BW,  and  i  miscellaneous,  but  including  pure  lea,  IcaXBW, 

etc. 


88 


INHERITANCE   IN   GUINEA-PIGS. 


In  each  array  of  animals  of  known  constitution  and  stock  the  number 
of  animals  involved,  the  mean  grade  of  dilution,  and  the  standard 
deviation  of  the  frequency  polygon  are  given.  It  will  be  noticed  that 
the  standard  deviations  decrease  as  the  analysis  is  made  closer.  For 


Red0     Red, 


White 


FIG.  5. — Variations  in  intensity  of  yellow.      Formula  and 
stock  printed  near  mode  of  each  distribution. 

example,  the  standard  deviation  for  all  dilute  blacks  is  1.53,  for  dilute 
blacks  of  formula  CdCa  is  1.13,  and  for  those  of  formula  CdCa  and  of 
South  American  stock  is  1.02.  The  corresponding  numbers  for  dilute 
yellows  are  1.10,  0.76,  and  0.59,  respectively. 


INHERITANCE   OF   MINOR   VARIATIONS   IN   INTENSITY. 


89 


In  tables  39  and  40  are  given  the  mean  grades  at  birth  and  when 
more  than  4  months  old  for  all  guinea-pigs  which  were  graded  these  two 
times.  These  data  are  arranged  by  constitution  and  stock.  In  most 
cases  the  mean  grade  at  birth  of  the  sample  graded  twice  agrees  well 
with  the  mean  grade  at  birth  of  the  whole  array  of  the  same  constitu- 
tion and  stock. 


BlacK 


SePa 


-Variations  in  intensity  of  dilute  blacks.     Formula  and  stock 
printed  near  mode  of  each  distribution. 

VARIATIONS  OF  YELLOW. 

I  owe  the  suggestion  that  heterozygous  albinism  may  be  correlated 
with  extreme  dilution  of  yellow  to  Professor  Castle,  who  found  that 
attempts  to  select  for  a  cream  stock  of  maximum  dilution  led  to  stocks 
which  invariably  gave  numerous  albinos.  The  tables  and  figures  con- 
firm this  suggestion  in  a  very  striking  way.  Animals  known  to  be 
homozygous  dilute  (CdCa)  vary  between  yellow2  and  yellow4  with  the 
mean  at  yellow2.9.  Those  known  to  transmit  albinism  vary  between 


90  INHERITANCE   IN   GUINEA-PIGS. 

TABLE  37. — Effects  of  stock  and  imperfect  dominance  on  intensity  of  yellow. 


Constitution. 

Stock. 

Redo 

Redi 

Y2 

Y, 

Y4 

Cr6 

Cr6 

Cr, 

No. 

Mean. 

<7 

Y 

Cr 

CdCd  

Dil  

1 
3 
10 

1 
2 
1 
9 
2 
3 
1 
3 
27 
19 
(3) 
(2) 
1 
7 
(1) 

2 
11 

12 
13 
37 
55 
8 
12 
57 

3.50 
2.64 
3.00 
4.31 
5.51 
5.54 
4.88 
4.75 
4.58 

0.50 
.77 
.41 
.46 
.60 
.71 
.33 
.43 
.59 

Do  

Misc  

6 
1 

6 

Do  

S.Am  

CdCr  

...Do  

4 
14 
23 
7 
9 
27 
20 
(3) 
(4) 
13 
19 

CdCa  

Dil  

21 
25 

4 

Do  

Misc  

1 

33 

Do  

JEW  

Do  

IBW  

Do  

S.Am      .  . 

3 
1 

1 
4 

(25  CdCr:  15  CdCa. 
iCdCr  by  test  

.  ..Do  

...Do  

(  CdCa  by  test  

.  ..Do  

12CdCd:23CdCa. 
(29  CdCd:  43  CdCa. 
i  CdCd  by  test  

Dil  

9 

20 

(2) 

12 

18 

Misc  

3 

(1) 

5 

4 
CD 

5 

.  ..Do  

[CdCa  by  test  

.  ..Do  

(4) 
3 

(3) 

(2) 

(2) 

2.5  CdCd:  3.5  CdCa. 
CdCd  

S.Am.BW. 
Total  

3 

7 

14 

4 
9 
36 
70 

25 
13 
169 
335 

2.88 
4.31 
5.12 
4.72 

.65 
.46 
.76 
1.10 

6 

CdCr  

.  ..Do  

4 
80 
128 

CdCa  

.  ..Do  

49 

77 

4 
7 

1 
10 

34 

41 

Dil  

.  ..Do  

9 

44 

TABLE  38. — Effects  of  stock  and  imperfect  dominance  on  intensity  of  black. 


Constitution. 

Stock. 

Bo 

Si 

82 

S3 

S4 

s» 

S6 

87 

S8 

No. 

Mean. 

<7 

CdCd  

Misc 

1 

6 

3 

1 

11 

2  45 

0  99 

Do  

S.Am.  . 

6 

4 

10 

1.40 

.50 

CdCr  

.  .  Do  .  .  . 

6 

7 

?, 

1 

1 

17 

2.06 

.94 

CrCr  

..Do..  . 

9, 

a 

4 

1.00 

1  00 

CdCa  

Misc.  .  . 

? 

4 

q 

?,3 

3 

41 

5.51 

1  05 

Do  

iBW  . 

7 

11 

17 

1 

36 

4.33 

82 

Do  

xBW 

i 

q 

2 

3 

15 

3.47 

88 

Do  

S.Am.  . 
.  .  Do  .  . 

2 

18 
16 

37 
94 

19 
17 

7 
17 

2 

4 

3 

85 
81 

4.20 
4  73 

1.02 
1  32 

(20  CdCd:  32  CdCa  

Misc.  .  . 

q 

9 

6 

8 

13 

7 

jCdCd  by  test  

.  .  Do  .  .  . 

C?1) 

[  CdCa  by  test  

.  .  Do  .  .  . 

CD 

CD 

C3) 

C?,) 

4  CdCd:  8  CdCa  

iBW  .. 

1 

i 

q 

1 

1.5  CdCd:  1.5  CdCa  

S.Am.  . 

1 

i 

1 

CdCa  bv  test  

.  .  Do  .  .  . 

CD 

29  CdCr:  20  CdCa  

..Do... 

10 

6 

9 

1?, 

4 

6 

?, 

CdCr  by  test  

..Do... 

Cfil 

CD 

C?r) 

CD 

CD 

CdCa  by  test  

.  .Do. 

C9) 

(2) 

C?t 

C9'* 

6  CrCr:  11  CrCa  

.  .  Do  .  .  . 

?, 

5 

?, 

3 

3 

?, 

CrCrby  test  

.  .Do.  .  . 

C?) 

CD 

CrCa  by  test  

.  .Do.  .  . 

CD 

CdCd  

Total.  . 

7 

10 

3 

1 

?1 

1.95 

95 

CdCr  

.  .Do..  . 

6 

7 

a 

1 

1 

17 

2.06 

.94 

CrCr  

.  .Do.  .  . 

0 

?, 

4 

1.00 

1.00 

CdCa  

.  .Do..  . 

3 

36 

f>4 

48 

31 

5 

177 

4.47 

1.13 

..Do.  . 

16 

94 

17 

17 

4 

3 

81 

4.73 

1.32 

CdrCdr  

.  .  Do  .  . 

9 

13 

19 

5 

1 

? 

4? 

1.90 

1  06 

CdrCa  

.  .  Do  .  . 

Ft 

5? 

78 

65 

48 

Q 

3 

958 

4.55 

1  20 

Dilute  

.  .  Do  .  . 

•>n 

34 

66 

70 

58 

45 

10 

303 

3.95 

1  53 

Red-eye  
Dil  +  RE  

..Do... 
..Do... 

2 
2 

20 

6 
40 

18 

84 

26 
96 

20 

78 

19 

64 

4 
14 

3 
3 

98 
401 

4.45 
4.07 

1.54 
1.53 

INHERITANCE   OF   MINOR   VARIATIONS   IN   INTENSITY. 


91 


yellow4  and  cream7,  mean  at  creams.!  very  distinctly  paler.  Litters 
which  should  give  both  have  given  the  entire  range  with  two  modes, 
at  yellow3  and  cream5,  respectively.  It  is  especially  to  be  noted  that 
among  13  of  these,  which  were  given  grades  before  their  constitution 
was  known,  4  ranging  from  yellow2  to  yellow4  proved  to  be  homozygotes, 
while  9  ranging  from  cream5  to  cream7  proved  to  be  heterozygotes. 
Dilutes  known  to  transmit  red-eye  (CdCr)  have  been  either  yellow4  or 
cream.5,  mean  at  yellow4.3.  These  should  be  compared  with  those  of 

TABLE  39. — Effect  of  age  on  intensity  of  yellow. 


Constitu- 
tion. 

Stock. 

Mean. 

No.  in 
sample. 

Mean 
at  birth. 

Mean 
adult. 

Dark- 
ening. 

CdCd  

Misc-Dil 

2.8 

9 

3.1 

2.9 

0.2 

CdCa  

Misc  .... 

5.5 

17 

5.1 

5.0 

.1 

Do  
Do  
Do  
CdCr  

Dil  
J-f  BW  . 
S.Am  .  .  . 
.  .  Do  

5.5 
4.8 
4.6 
4.3 

9 
11 
9 
5 

5.2 
5.0 

4.4 
4.8 

6.0 

4.7 
4.7 
4.2 

-    .8 
.3 
-    .3 
.6 

TABLE  40. — Effect  of  age  on  intensity  of  black. 


Constitu- 
tion. 

Stock. 

Mean. 

No.  in 
sample. 

Mean 
at  birth. 

Mean 
adult. 

Dark- 
ening. 

CdCd  
CdCa  

Misc  .... 
.  .Do 

2.5 
5.5 

8 
14 

3.0 
5.6 

2.4 
4.6 

0.6 
1.0 

Do  
Do  
Do  

£BW.... 
fBW.... 
S.Am  .  .  . 
.  .  Do  

4.3 
3.5 

4.2 

4.7 

20 
6 
15 

8 

4.3 
3.3 

4.8 
4.9 

3.2 
2.5 
3.3 
2.0 

1.1 
.8 
1.5 
2.9 

CdCr  

.  .Do  

2.1 

16 

2.2 

1.1 

1.1 

CrCr  

.  .Do  

1.0 

4 

1.0 

1.0 

0 

the  same  stock  (S.  Am.)  which  transmit  albinism.  The  difference, 
yellow4.3  compared  with  yellow4.6,  is  too  small  to  be  relied  on.  Litters 
which  should  give  both  CdCr  and  C<jCa  have  given  a  range  of  yellow4  to 
creame,  as  expected.  Thus  grade  yellow4  may  be  any  sort  of  a  dilute; 
one  more  intense  is  quite  certain  to  be  homozygous  (CdCd) ;  one  more 
dilute  is  quite  certain  to  transmit  either  red-eye  or  albinism. 

The  influence  of  stock  can  only  be  recognized  surely  in  the  case  of 
those  known  to  be  CdCa.  The  numbers  are  too  small  among  the 
homozygotes.  Among  the  heterozygotes  (CdCa)  it  is  clear  that  those  of 
dilute  and  miscellaneous  stocks,  both  with  a  mean  of  cream5.5,  are 
distinctly  paler  than  those  with  an  admixture  of  BW  or  S.Am.  blood 
with  means  from  cream^g  to  cream^g. 

The  data  in  table  39  indicate  that  yellow  undergoes  no  appreciable 
change  in  intensity  during  the  life  of  an  animal,  except  in  the  dilute 
selection  stock.  In  this  case  there  is  a  change  from  cream5.2  at  birth 
to  creamy  when  adult,  among  those  carrying  albinism. 


92  INHERITANCE   IN   GUINEA-PIGS. 

VARIATIONS  OF  SEPIA. 

We  find  rather  more  overlapping  of  distributions  among  the  sepias 
than  among  the  yellows  when  different  genetic  constitutions  are  com- 
pared. Nevertheless  there  are  significant  differences  in  the  means. 
The  groups  CdCd,  CdCr,  and  CrCr  with  means  from  sepia!  to  sepia^.i, 
nearly  black,  average  distinctly  darker  than  groups  CaCa  and  CrCa  with 
means  of  sepia4.5  and  sepia4.7,  respectively.  The  case  is  quite  different 
from  yellow  dilution  in  which  CdCr  and  CaCa  have  the  same  effect  (or 
nearly  so)  contrasting  with  CdCd-  Cr  seems  to  be  essentially  identical 
with  Cd  in  effect  on  black,  but  like  Ca  in  effect  on  yellow. 

For  further  analysis  we  must  compare  stocks.  In  the  miscellaneous 
stock  the  average  for  C<jCa  is  sepia5.5.  When  this  stock  is  crossed  with 
albinos  of  BW  stock  the  average  of  the  young — again  C<jCa — is  sepia4.3. 
When  these  are  crossed  again  with  BW  albinos  the  average  becomes 
sepia3.5.  The  darkening  influence  of  the  BW  stock  is  apparent.  The 
South  American  stock  also  has  a  darkening  influence  with  an  average 
of  sepia4.2.  We  find  a  similar  difference  between  the  miscellaneous  and 
South  American  stocks  among  the  homozygotes. 

The  comparison  of  CdCa  with  CrCa  within  the  same  stock  (South 
American)  yields  a  slight  but  probably  significant  difference  (CdCa, 
sepia4.2;  CrCa,  sepia47).  Thus  there  is  a  difference  of  0.5  with  a  prob- 
able error  of  0.12.  It  is  certain  that  some  of  the  red-eyed  sepias  have 
been  paler  than  any  black-eyed  sepia. 

If  there  is  a  real  difference  here,  we  would  expect  CrCr  to  be  lighter 
than  CdCd  or  CdCr,  but  the  4  individuals  known  to  be  CrCr  give  the 
darkest  average  of  any  array.  They  were  not,  however,  a  random 
sample  and,  further,  were  either  pure  lea  or  F2  IcaXBW  and  hardly 
to  be  compared  in  stock  with  those  known  to  be  CdCd  or  CdCr.  For 
the  present  CdCd,  CdCr,  and  CrCr  may  be  considered  identical  in  effect 
on  black  fur. 

As  in  the  case  of  yellows,  the  most  critical  test  of  the  hypothesis  of 
imperfect  dominance  is  the  success  of  prophecy.  In  litters  which 
should  give  both  CdCd  and  CdCa,  the  2  darkest  tested  (sepia^)  both 
proved  to  be  homozygous,  while  8  others  (sepia4  to  sepia?)  proved  to 
transmit  albinism.  Among  those  which  when  graded  might  be  either 
CdCr  or  CdCa,  18  were  tested.  There  is  some  overlapping  of  ranges,  but 
those  which  were  found  to  transmit  red-eye  average  very  distinctly 
darker  than  those  which  transmitted  albinism.  Four  were  tested  in  an 
F2  from  red-eye  by  albino.  The  3  dark  ones,  including  2  which  were 
actually  as  black  as  blacks  of  the  BW  race,  proved  to  be  CrCr,  while 
the  other,  sepia4,  had  albino  young  and  was  therefore  CrCa. 

Table  40  shows  that  in  the  case  of  the  sepias  there  is  a  very  perceptible 
darkening  with  age.  This  is  shown  in  all  groups  except  the  homozy- 
gous red-eyes,  which  were  practically  jet  black  to  begin  with.  Another 
interesting  point  brought  out  is  a  race  difference  in  the  amount  of 


INHERITANCE    OF   MINOR    VARIATIONS   IN   INTENSITY.          93 

darkening.  The  darkening  was  about  1.0  among  40  animals  CaCa 
without  South  American  blood,  although  with  considerable  BW  blood 
in  most  cases;  among  23  animals  CdCa  or  CrCa,  with  South  American 
blood,  the  average  darkening  is  2.0 — twice  as  much.  One  case  among 
the  latter  was  very  striking.  Male  D238,  a  red-eyed  sepia,  CrCa,  was 
the  palest  sepia  recorded.  The  tip  of  the  hair  was  called  sepias ;  the 
base  was  nearly  white.  When  2  months  old,  most  of  the  hah*  was  still 
of  this  pale  color,  but  there  were  sharply  contrasting  areas  which  were 
nearly  black  (sepi^)  on  the  nose,  in  spectacles  around  the  eyes,  in  front 
of  the  ears,  on  the  feet,  and  in  an  asymmetrical  patch  on  the  back.  At 
the  age  of  4  months,  most  of  the  fur  on  the  back  was  sepia^,  although 
the  belly  remained  fairly  light.  In  the  lea  and  Arequipa  stocks  the 
dark  color  always  appears  first  on  the  nose,  feet,  and  ears.  These 
are  the  darkest  regions  generally  in  all  dilutes,  a  fact  which  recalls  the 
location  of  the  dark  smudges  in  sooty  albino  guinea-pigs  and  Hima- 
layan rabbits.  In  adult  animals  with  a  large  amount  of  South  Ameri- 
can blood,  the  darkening  with  age  is  so  great  that  CarCar  can  seldom 
be  distinguished  from  CarCa,  although  quite  reliable  predictions  could 
be  made  at  birth  as  to  the  nature  of  the  same  animals. 

VARIATIONS  OF  EYE  COLOR. 

The  variations  of  eye  color  have  not  been  studied  as  carefully  as  those 
of  yellow  and  sepia  fur  colors.  In  intense  guinea-pigs  (C-)  the  eye 
ordinarily  appears  black  (factors  B  and  P  of  course  assumed  to  be 
present  as  throughout  the  discussion  of  dilution);  in  many  cases, 
however,  it  is  possible  in  the  proper  light  to  obtain  a  red  reflection 
through  the  pupil.  In  dilute  guinea-pigs  CaCa,  CaCr,  or  CaCa,  the 
eye  also  appears  black  ordinarily,  but  a  red  reflection  seems  to  be 
obtained  more  easily  as  a  rule  than  in  intense  guinea-pigs.  The  differ- 
ence is  not  great  enough  to  be  of  value  as  a  criterion.  In  guinea-pigs 
which  are  CrCr  or  CrCa  the  pupil  appears  red  in  most  lights  and  usually 
the  inner  ring  of  the  iris  is  transparent  and  also  appears  red.  In  very 
few,  if  any,  cases  is  the  eye  so  dark  that  confusion  with  a  dilute  or 
intense  is  possible.  There  is  much  variation  in  the  amount  of  pigment 
present.  These  variations  are  probably  connected  with  differences  in 
stock  and  possibly  imperfect  dominance  of  Cr  over  Ca.  No  pigment 
has  been  noted  in  the  pink  eyes  of  albinos.  A  red-eye  can  never  be 
confused  with  a  pink-eyed  type,  unless,  of  course,  factor  p  is  present. 

SUMMARY. 

1.  First-order  effects  in  the  dilution  of  yellow  are  due  to  the  presence 
of  various  combinations  of  factors  of  the  albino  series  of  allelomorphs. 
The  red-eye  and  albino  factors  (Cr  and  Ca  respectively),  produce  nearly 
if  not  quite  identical  effects.  In  the  case  of  black,  first-order  effects 
may  be  due  either  to  different  combinations  in  the  albino  series  or  to 


94 


INHERITANCE   IN   GUINEA-PIGS. 


independent  factors  (p).  In  the  albino  series,  the  dilution  and  red-eye 
factors  (Cd  and  Cr  respectively)  produce  nearly  if  not  quite  identical 
effects.  In  eye  pigmentation,  as  in  the  black  pigmentation  of  the  fur, 
first-order  effects  may  be  due  either  to  different  combinations  in  the 
albino  series  or  to  other  factors  (p) ;  but  there  is  a  sharp  difference  from 
the  effects  on  black  fur,  in  that  the  dilution  and  red-eye  factors  produce 
very  different  effects.  In  this  case  the  intensity  and  dilution  factors 
apparently  produce  nearly  identical  effects. 

TABLE  41. 


Yellow  fur. 

Black  fur. 

Black  eye. 

Formula. 

Color. 

Formula. 

Color. 

Formula. 

Color. 

C-  

Red  

C-   

Black  

C-  

Black. 
Nearly  black. 
Red. 
Pink. 

CdCd... 
CdCra-  •  • 
CraCra-  • 

Yellow.  .. 
Cream  .  .  . 
White.... 

CdrCdr... 
CdrCa-  •  •  • 
CaCa.  .  .  • 

Dark  sepia  . 
Light  sepia  . 
White 

Cd  

Cr  

CaCa  .... 

2.  Second-order  effects  in  dilution  of  yellow,  black,  and  probably 
eye-color,  are  due  to  the  unanalyzed  residual  heredity  of  different  stocks. 
In  the  stock  at  the  Bussey  Institution  BW  and  South  American  blood 
intensify  as  compared  with  dilute  selection  or  4-toe  blood.     This  resid- 
ual heredity  seems  to  be  more  important  in  the  case  of  black  than 
yellow,  producing  more  overlapping  of  the  ranges  of  the  different  albino 
series  combinations. 

3.  In  only  one  stock  has  the  intensity  of  yellow  at  birth  been  observed 
to  change  appreciably  in  the  lifetime  of  the  animal.     In  this  case,  the 
dilute  selection  stock,  the  creams  grow  paler  as  they  grow  older.    Sepia, 
on  the  other  hand,  grows  distinctly  darker  as  the  animals  grow  older  in 
all  stocks.     In  the  imported  South  American  stocks  this  darkening  is 
so  pronounced  that  adults  of  any  albino  series  combination,  except 
albinism  itself  (CaCa),  are  practically  black. 

INHERITANCE  OF  VARIATIONS  IN  THE  AGOUTI  PATTERN. 

Most  wild  rodents  and  many  other  mammals  have  a  coat  color  of 
the  agouti  type,  viz,  a  predominantly  black  fur  in  which  each  hah* 
has  a  subterminal  yellow  band.  In  many  cases,  as  in  the  mouse  and 
rat,  the  entire  coat  is  fairly  uniform  in  appearance.  This  is  not  true 
in  all  cases,  however.  The  color  of  Cavia  cutleri  has  been  described 
at  the  beginning  of  this  paper.  It  will  be  recalled  that  the  color  of  the 
belly  is  sharply  distinct  from  that  of  the  back,  appearing  wholly  yellow 
instead  of  ticked.  Tame  guinea-pigs  of  the  agouti  variety  likewise 
have  this  so-called  light-bellied  type  of  agouti. 


VARIATIONS   IN   AGOUTI   PATTERN.  95 

The  agouti  pattern  of  mice  was  shown  by  Cue"  not  hi  1903  to  be  a 
unit  Mendelian  character  dominant  over  its  absence  as  found  in  blacks. 
In  this  and  later  papers  (1903,  1904,  1907)  he  demonstrated  that  a 
white-bellied  type  of  agouti  and  self  yellow  are  due  to  members  of 
the  same  series  of  allelomorphs.  Castle,  1905,  demonstrated  that 
guinea-pig  agouti  is  a  simple  dominant  over  non-agouti. 

This  agouti  pattern  of  guinea-pigs  is  subject  to  considerable  varia- 
tion. In  some  cases  the  belly  hairs  are  entirely  yellow,  a  condition 
correlated  with  very  broad  yellow  ticking  in  the  dorsal  fur.  At  the 
other  extreme,  the  base  of  the  hairs  on  the  belly  is  black  for  about  half 
the  length,  and  the  dorsal  ticking  is  markedly  decreased.  This  dark 
type  has  been  produced  by  repeated  crossing  with  intense  blacks 
(BB  race).  Although  distinctly  darker  than  usual,  all  of  the  agoutis 
from  such  crosses  are  distinctly  yellow-bellied. 

PREVIOUS  WORK. 

Detlefsen  (1914)  made  experiments  with  the  wild  species  Cavia  rufes- 
cens  of  Brazil.  This  has  the  agouti  pattern,  but  is  somewhat  darker 
than  C.  cutleri  or  the  tame  guinea-pig.  The  yellow  bands  in  the  dorsal 
fur  are  narrower  and  there  is  usually  more  black  on  the  belly,  which 
indeed  is  usually  slightly  ticked  with  black.  The  difference  in  appear- 
ance is  not  very  great.  Detlefsen  found,  as  he  expected,  that  C. 
rufescens  was  homozygous  for  the  agouti  factor.  In  the  hybrids 
between  C.  rufescens  and  black  guinea-pigs,  the  agouti  behaved  as  a 
simple  Mendelian  dominant.  What  was  not  expected  was  a  marked 
darkening  of  the  agoutis  which  occurred  among  the  hybrids  in  many 
cases.  The  yellow  subterminal  bands  became  so  reduced  on  the  back 
that  many  of  the  agoutis  appeared  more  like  blacks  than  guinea-pig 
agoutis  at  birth.  Black  appeared  at  the  ends  of  the  hairs  on  the  belly, 
and  the  appearance  changed  from  yellow  to  ticked.  In  the  early 
generations  the  variations  hi  the  agouti  were  exceedingly  erratic  in 
their  hereditary  behavior.  Light-bellied  hybrids  crossed  with  blacks 
often  gave  ticked-bellied  young,  and  ticked-bellied  hybrids  gave  light- 
bellied  young.  Nevertheless,  as  more  guinea-pig  blood  was  introduced 
by  repeated  back-crosses,  the  trend  was  constantly  toward  the  ticked- 
bellied  type.  In  lines  hi  which  the  ticked-bellied  type  had  become 
constant,  crosses  were  made  with  typical  light-bellied  agouti  guinea- 
pigs.  The  ticked-bellied  type  was  found  to  be  recessive  and  segregated 
out  in  later  crosses  in  regular  fashion.  Detlefsen  found  that  the  results 
in  these  lines  were  adequately  explained  by  assuming  that  the  ticked- 
bellied  type  is  due  to  an  allelomorph  of  both  the  light-bellied  agouti 
factor  and  the  non-agouti  factor,  recessive  to  the  former,  dominant  to 
the  latter.  He  used  the  nomenclature  A,  A',  and  a  for  the  tame  agouti, 
wild  agouti,  and  non-agouti  factors,  respectively. 


96 


INHERITANCE   IN    GUINEA-PIGS. 


THE  INHERITANCE  OF  THE  AGOUTI  OF  CAVIA  RUFESCENS. 

The  writer  has  had  the  opportunity  of  experimenting  with  the  hybrid 
rufescens  stock  developed  by  Dr.  Detlefsen.  As  the  mode  of  inherit- 
ance of  the  type  of  agouti  is  of  special  interest  in  being  a  character  in 
which  two  wild  species  differ,  it  seemed  worth  while  to  obtain  additional 
data.  New  crosses  were  made  to  test  out  the  hypothesis  of  triple 
allelomorphs  as  thoroughly  as  possible.  It  may  be  said  at  once  that 
the  results  obtained  completely  confirm  Detlefsen's  hypothesis. 

When  received  by  the  writer,  there  were  only  2  light-bellied  agouti 
hybrids  in  the  stock  which  had  derived  their  agouti  from  C.  rufescens. 
These  were  A606  and  A450,  |  and  |  blood  hybrids,  respectively.  They 
were  crossed  with  black  guinea-pigs  and  one  litter  was  obtained  from 
each — 2  blacks  from  A606  and  1  light-bellied  agouti  and  1  black  from 
A450.  This  light-bellied  agouti  son  unfortunately  proved  to  be  sterile, 
so  that  experiments  with  light-bellied  rufescens  agouti  came  to  an  end. 
Only  one  light-bellied  agouti — born  dead — has  appeared  since  then  which 
seemed  to  derive  its  agouti  from  C.  rufescens,  and  in  this  case  the 
parentage  was  doubtful.  Thus  in  the  following  experiments,  rufescens 
agouti  and  ticked-bellied  agouti  are  practically  equivalent.  It  must 
be  emphasized  that  this  was  not  the  case  in  Detlefsen's  experiments, 
so  that  the  following  results  are  simpler  than  those  which  he  encoun- 
tered in  the  earlier  generations. 

Let  us  consider  first  the  relations  of  rufescens  agouti  and  guinea-pig 
non-agouti.  Cross  1  gives  matings  of  non-agoutis  with  ticked-bellies 
known  to  be  heterozygous  because  of  a  non-agouti  parent  (table  42). 

TABLE  42. 


Female. 

Male. 

Agouti 
light- 
belly. 

Agouti 
ticked- 
belly. 

Non- 
agouti. 

la 

Non-agouti  (g.  p.) 

X  agouti  ticked-belly  

62 

62 

16 

Non-agouti  (hybrid) 

X  agouti  ticked-belly  

17 

13 

Ic 

Non-agouti 

X  A'a  (red  or  white)  

11 

12 

Id 

Agouti  ticked-belly 

X  non-agouti  (g.  p.)  

1 

61 

63 

le 

Agouti  ticked-belly 

X  non-agouti  (hybrid)  

10 

5 

1 

161 

155 

The  single  agouti  light-belly  was  the  son  of  A450,  mentioned  above, 
which,  though  agouti  light-belly,  is  included  under  agouti  ticked-belly 
as  a  rufescens  agouti.  The  cross  shows  that  ticked-belly  is  a  simple 
dominant  over  non-agouti.  The  ratio  of  agouti  ticked-belly  to  non- 
agouti  is  sufficiently  close  to  a  1  to  1  ratio.  If  ticked-bellied  agouti  were 
due  to  independent  modifying  factors  or  to  the  residual  heredity  of 
C.  rufescens,  acting  with  the  same  agouti  factor  as  found  in  C.  cutleri 
and  C.  porcellus,  non-agouti  guinea-pigs  should  possess  factors  tending 


VARIATIONS   IN   AGOUTI   PATTERN. 


97 


to  change  ticked-bellied  agouti  to  the  typical  light-bellied  type.  The 
crosses  show  conclusively  that  they  possess  no  such  tendency.  Indeed 
when  it  is  recalled  that,  hi  the  early  hybrids  and  C.  rufescens  itself, 
light-belly  was  common,  it  seems  necessary  to  suppose  that  guinea-pigs 
possess  a  residual  heredity  which  tends  to  darken  agouti. 

Ticked-bellied  agoutis,  known  to  be  heterozygous  because  of  parent- 
age, were  crossed  inter  se.  The  results  are  given  in  cross  2. 

Aglb.         Agtb.         Non-ag. 
Agtb.  X  Agtb 0  66  19 

This  result  is  sufficiently  close  to  the  expected  3  to  1  ratio.  One- 
third  of  the  ticked-bellied  young  from  this  cross  should  be  homozygous 
(A'A')  and  two- thirds  heterozygous  (A'a).  Several  of  them  have  been 
tested  by  crosses  with  blacks  (cross  3,  table  43) . 

TABLE  43. 


Female. 

Male. 

Agouti 
light- 
belly. 

Agouti 
ticked- 
belly. 

Non- 
agouti. 

3a 

7  agouti  ticked-belly 

X  Non-agouti  

10 

11 

3c 

Non-agouti 

X  9  agouti  ticked-belly  

1 

40 

38 

36 

5  agouti  ticked-belly 

X  Non-agouti  

25 

3d 

Non-agouti 

X  1  agouti  ticked-belly  

12 

The  single  agouti  light-belly  was  the  one  of  doubtful  parentage  men- 
tioned above.  Sixteen  heterozygotes  were  obtained  which  gave  agouti 
ticked-belly  and  non-agouti  in  approximately  equal  numbers;  6  possible 
homozygotes  were  obtained,  rather  fewer  than  is  to  be  expected.  The 
male  AA253  with  12  agouti  ticked-belly  young  and  2  females,  AA213 
and  AA217,  with  8  agouti  ticked-belly  young  each,  were  quite  certainly 
homozygous  and  were  used  to  establish  a  homozygous  ticked-bellied 
stock.  They  and  their  progeny  crossed  inter  se  have  given  only  ticked- 
bellies,  26  in  number  (cross  4).  These  homozygous  ticked-bellies  are 
indistinguishable  from  heterozygotes  in  appearance. 

Cross  6  gives  matings  of  homozygous  light-bellied  agouti  guinea-pigs 
with  non-agouti  hybrids.  The  young,  29  in  number,  are  all  light- 
bellied.  There  is  no  tendency  toward  ticked-belly  introduced  by  the 
hybrids. 

Cross  7  gives  matings  of  light-bellied  hybrids  (agouti  derived  from 
guinea-pigs)  with  non-agoutis.  All  of  these  light-bellies  were  known 
to  be  heterozygous  from  their  parentage.  The  result,  18  light-bellies, 
21  non-agoutis,  no  ticked-bellies,  is  in  harmony  with  expectation 
(19.5  : 19.5). 

Crosses  8  and  9  give  data  on  the  relation  of  light-belly  to  ticked-belly. 
Homozygous  light-bellied  guinea-pig  by  ticked-bellied  hybrid  gives 
exclusively  light-bellies,  50  hi  number.  Light-belly  is  thus  clearly 


98  INHERITANCE    IN   GUINEA-PIGS. 

dominant.  Heterozygous  light-belly  (with  a  non-agouti  parent)  by 
heterozygous  ticked-belly  (also  with  a  non-agouti  parent)  gave  16 
light-bellied,  6  ticked-bellied,  and  10  non-agouti  young  where  expecta- 
tion is  16  :  8  :  8. 

The  results  given  so  far  show  that  light-belly  is  dominant  or  at  least 
epistatic  over  ticked-belly,  that  ticked-belly  is  a  simple  Mendelian 
dominant  over  non-agouti,  and  that  the  difference  between  rufescens 
and  porcellus  agouti  is  not  a  question  of  residual  heredity.  The  fact 
that  crossing  with  guinea-pig  non-agouti  increases  the  difference  be- 
tween rufescens  and  porcellus  agouti,  instead  of  destroying  it,  shows 
that  rufescens  agouti  does  not  contain  the  same  agouti  factor  as  is  found 
in  guinea-pig  agoutis.  Rufescens  agouti  must  have  an  allelomorph  of 
guinea-pig  agouti,  recessive  to  the  latter.  This  leaves  two  possibilities. 
This  allelomorph  may  be  (I)  the  non-agouti  factor  or  (II)  a  new  allelo- 
morph recessive  to  the  porcellus  agouti  factor,  dominant  to  non-agouti 
(Detlef sen's  hypothesis).  Both  of  these  explanations  fit  equally  well 
all  of  the  data  given  so  far.  Under  (I)  a  guinea-pig  light-belly  is 
AAa'a',  a  non-agouti  aaa'a',  and  a  rufescens  agouti  aaA'A'.  Under  (II) 
these  three  varieties  are  AA,  aa,  and  A'A',  respectively.  The  critical 
test  is  whether  it  is  possible  to  produce  light-bellies  which  are  double 
heterozygotes  AaA'a',  capable  of  having  both  ticked-bellied  and  non- 
agouti  young,  as  well  as  light-bellies  when  crossed  with  non-agoutis. 
Detlefsen  obtained  5  light-bellied  agoutis  from  the  cross  light-belly  by 
heterozygous  ticked-belly  which  bear  on  this  point.  Each  of  these  had 
ticked-bellied  young,  but  no  non-agoutis.  They,  therefore,  point 
toward  hypothesis  (II),  which  is  also  more  probable  a  priori.  They 
had,  however,  only  from  3  to  6  young,  21  in  all,  so  that  it  is  not  wholly 
certain  that  they  would  have  had  no  non-agouti  young  if  tested  further. 
This  point,  therefore,  seemed  to  the  writer  to  be  one  on  which  additional 
data  would  be  desirable,  and  special  attention  has  been  paid  to  it. 

The  cross  heterozygous  ticked-belly  by  heterozygous  light-bellies 
known  from  their  parentage  to  be  free  from  ticked-belly  can  be  repre- 
sented as  follows  under  the  two  hypotheses : 

Agtb.          Aglb.          Aglb.          Aglb,          Agtb.          Non-ag. 
(I)  aaA'a'  X  Aaa'a'  =  AaA'a'  +  Aaa'a'  +  aaA'a'  +  aaa'a'. 
(II)  A'a        X  Aa         =  AA'        -f  Aa         +  A'a        +  aa 

In  both  cases  we  expect  2  light-bellies  to  1  ticked-belly  to  1  non- 
agouti.  Under  (I)  the  light-bellied  young  which  can  transmit  ticked- 
belly  (AaA'a)  must  also  have  the  power  of  transmitting  non-agouti. 
Under  (II)  such  light-bellies  (AA')  should  not  transmit  non-agouti. 
Under  (II)  half  of  the  light  bellies  should  be  of  this  type  and  the  other 
half  should  transmit  non-agouti  but  not  ticked-belly  (Aa).  Thus,  if 
a  large  number  of  young  can  be  obtained  from  a  light-belly  from  such 
a  cross,  which  has  had  ticked-bellied  young  in  crosses  with  non-agoutis, 
the  presence  or  absence  of  non-agouti  young  is  decisive  between  the 


VARIATIONS   IN   AGOUTI   PATTERN. 


99 


two  hypotheses.     Cross  10  gives  the  results  of  the  tests  of  light-bellied 
young  from  such  a  cross  as  described  (table  44). 


TABLE  44. 


Females. 

Males. 

Aglb. 

Agtb. 

Non-ag. 

10a 

7  aglb.  .. 

Non-ag  .  . 

17 

20 

lOc 

Non-ag  .  . 

4  aglb  

26 

33 

106 

10  aglb... 

Non-ag  .  . 

18 

30 

lOd 

Non-ag  .  . 

5  aglb  

45 

50 

In  no  case  has  the  same  animal  had  both  ticked-bellied  and  non- 
agouti  young.  Some  of  those  which  have  had  ticked-bellied  young 
have  been  quite  thoroughly  tested.  Male  M138  had  20  light-bellied 
and  19  ticked-bellied  young.  Male  B121  had  13  light-bellied  and  13 
ticked-bellied  young.  Male  M91  had  5  light-bellied  and  11  ticked- 
bellied  young.  The  chance  that  these  can  represent  2:1:1  ratios  is 
negligible.  Thus  hypothesis  (I)  may  be  dismissed. 

Light-bellied  agoutis  demonstrated  to  carry  ticked-belly  have  been 
crossed  inter  se  (cross  11).  They  have  given  25  light-bellies  and  9 
ticked-bellies,  no  non-agoutis.  This  agrees  reasonably  well  with  the 
expected  3  to  1  ratio.  The  remaining  tables  give  the  results  of  miscel- 
laneous crosses.  All  of  them  are  in  harmony  with  the  hypothesis  of 
triple  allelomorphs. 

MINOR  VARIATIONS. 

Thus  there  seems  no  doubt  that  the  light-bellied  agouti  of  Cavia 
porcellus,  the  ticked-bellied  agouti  of  C.  rufescens  hybrids,  and  non- 
agouti  form  a  series  of  triple  allelomorphs.  The  question  remains 
whether  light-bellied  Cavia  rufescens  hybrids  possess  a  different  allelo- 
morph from  the  ticked-bellied  ones,  or  whether  the  difference  lies 
simply  in  the  residual  heredity.  There  are  no  wholly  satisfactory  data 
bearing  on  this  point.  Nevertheless  the  fact  that  the  darkening  seems 
associated  especially  with  certain  stocks  of  guinea-pigs  seems  to  favor 
the  second  view.  The  writer  has  crossed  ticked-bellied  agoutis  re- 
peatedly with  the  intense  blacks  of  BB  or  BW  stock.  Young  have 
been  obtained  which  were  self  black,  except  for  a  few  ticked  hairs  in  the 
chest  and  whiskers.  One  ignorant  of  their  history  would  probably 
have  classified  several  of  them  as  blacks.  Before  they  became  adult, 
however,  these  black  ticked-bellies  acquired  a  uniform  though  very 
slight  yellow  ticking  throughout  the  entire  fur.  On  crossing  such  black 
ticked-bellies  with  a  dull  black  stock  (4-toe)  there  is  a  return  to  a  more 
strongly  developed  agouti  pattern.  The  young  are  uniformly  ticked 
when  born.  Thus  these  variations  in  the  agouti  pattern  seem  related 
to  the  residual  heredity  of  the  stocks,  possibly  with  the  same  residual 
heredity  which  determines  the  very  intense  development  of  pigment, 


100  INHERITANCE   IN    GUINEA-PIGS. 

especially  black,  in  the  BB  and  BW  races,  the  feebler  development  in 
the  4-toe  race,  and  the  much  feebler  development  in  the  wild  species. 
If  this  is  correct,  the  resemblance  of  light-bellied  rufescens  to  light- 
bellied  agoutis,  like  that  of  the  pale  color  of  C.  cutleri  to  dilute  guinea- 
pigs,  is  secondary.  In  both  cases  the  wild  species  possess  a  different 
allelomorph  from  the  guinea-pig  in  the  principal  series  of  factors 
involved,  but  owing  to  different  residual  heredity,  have  a  superficial 
resemblance. 

THE  INHERITANCE  OF  THE  AGOUTI  OF  CAVIA  CUTLERI. 

The  writer  has  had  the  opportunity  of  working  with  the  agouti  of 
Cavia  cutleri.  Repeated  crosses  have  been  made  with  blacks  of  the 
BW  race  of  guinea-pigs  to  see  whether  a  ticked-bellied  agouti  could  be 
obtained.  While  some  ventral  ticking  has  been  observed  in  some  cases, 
the  f-blood  cutleri  hybrids  are  still  on  the  whole  good  light-bellied 
agoutis.  The  cutleri  agouti  is  unquestionably  more  resistant  to  dark- 
ening influences  than  was  rufescens  agouti.  No  results  have  been 
obtained  yet  which  serve  to  differentiate  it  from  the  guinea-pig  agouti. 
This  is  additional  evidence  that  C.  cutleri  was  ancestral  to  porcellus. 
The  experimental  results  are  given  in  crosses  68  to  78. 

Only  one  cross  has  been  made  between  a  cutleri  and  ticked-bellied 
rufescens  hybrids.  Male  K56,  a  black  J  cutleri  (f  4-toe),  was  crossed 
with  two  ticked-bellied  agoutis,  which  of  course  had  some  rufescens 
ancestry.  There  were  6  young  (3  blacks  and  3  ticked-bellies)  of  which 
one  was  quite  light  and  one  was  black,  except  for  a  few  ticked  hairs  on 
the  chest  and  whiskers.  There  was  thus  no  very  conspicuous  tendency 
toward  light-belly  introduced  by  the  cutleri  hybrid.  It  seems  safe  to 
assume  that  C.  cutleri  has  a  different  member  of  the  agouti  series  of 
allelomorphs  from  C.  rufescens,  but  the  same  or  nearly  the  same  as 
C.  porcellus. 

Wild  species  of  the  same  genus  seldom  differ  as  much  superficially 
hi  any  one  character  as  do  many  varieties  of  domesticated  animals. 
Yet  while  very  large  variations  in  the  latter  have  been  shown  in  many 
cases  to  behave  as  simple  Mendelian  units  in  inheritance,  the  char- 
acters by  which  wild  species  differ  usually  seem  to  be  highly  complex 
in  heredity.  Few  well-defined  Mendelian  factors  are  recorded  in  the 
literature  of  hybridization.  It  is,  therefore,  interesting  to  find  that  the 
darker  agouti  of  Cavia  rufescens  differs  from  the  lighter  agouti  of  C. 
cutleri  by  a  clear-cut  Mendelian  factor. 
illttHf'''^ 

INHERITANCE  OF  ROUGH  FUR. 

In  the  wild  species  of  cavy,  and  in  the  ordinary  smooth  guinea-pigs, 
the  hair  shows  a  definite  direction  of  growth,  which  is  always  away 
from  the  snout  on  the  body  and  toward  the  toes  on  the  legs.  This  is  at 
least  the  general  tendency  of  the  hair  in  most  mammals,  and  it  is 


ROUGH   FUR.  101 

obviously  the  most  advantageous;  the  hair  lying  thus  is  not  ruffled  or 
caught  by  obstacles  when  the  animal  is  moving.  This  direction  is  not 
directly  imposed  on  the  hair  by  outside  agencies,  as  might  be  supposed, 
but  is  due  to  the  direction  of  growth  of  the  hair  follicles  (Wilder,  1909). 

Certain  fancy  varieties  among  guinea-pigs,  as  the  long-haired  rough 
"  Peruvians  "  and  the  short-haired  rough  "  Abyssinians,"  show  a  striking 
deviation  from  the  normal  hah*  direction.  In  these  varieties  the  coat 
can  be  divided  into  a  number  of  areas,  within  each  of  which  all  hair 
directions  radiate  from  a  definite  center.  The  boundaries  of  these 
areas,  where  contrary  hair-currents  meet,  are  marked  by  crests.  The 
centers  with  their  radiating  hair-currents  are  called  rosettes.  Many 
mammals,  including  man,  naturally  show  rosettes,  crests,  or  other 
peculiarities  of  hair  direction,  but  less  conspicuously  than  the  rough 
guinea-pigs.  (See  plate  7.) 

The  positions  in  which  rosettes  may  occur  in  guinea-pigs  are  quite 
definite.  Following  are  the  rosettes  and  irregularities  given  by  Castle 
(1905),  with  the  addition  of  L,  irregular  roughness  on  the  chest. 

A.  Forehead,  unpaired.  E.  Sides,  between  shoulder  and  hip.  I.  Navel,  unpaired. 

B.  Eyes.  F.  Hips.  J.  Front  toes. 

C.  Ears.  G.  Above  the  groin.  K.  Hind  toes. 

D.  Shoulders.  H.  Mammae.  L.  Irregular  roughness  of  chest. 

In  the  grading  of  the  young  guinea-pigs,  large  letters,  as  above,  have 
been  used  for  well-defined  rosettes  and  small  letters  for  feeble  rosettes 
or  slight  deviations  from  normal  hair  direction  in  an  area,  indicated 
only  by  crests  at  a  boundary.  Thus  a  mid-dorsal  crest  or  mane  (e) 
without  any  side  or  hip  rosettes  is  characteristic  of  a  certain  grade  of 
partial  roughs.  The  ear  rosettes  (C)  are  usually  only  revealed  by  a 
crest  between  the  ears.  The  shoulder  rosettes  are  seldom  well  developed. 
The  side  rosettes  are  sometimes  doubled  in  the  roughest  animals  (E,E2) . 

The  number  of  rosettes  present  varies  from  the  full  set  described 
above,  through  a  continuous  series  of  intermediate  grades,  to  one  pan*. 
The  variations  are  not  merely  haphazard,  but  may  easily  be  classified. 
In  the  first  place,  it  is  necessary  to  distinguish  two  series.  A  slight 
roughness  found  in  certain  stocks  (the  BW,  lea,  and  Arequipa  stocks) 
does  not  fit  into  the  usual  series  of  variations  and  will  be  discussed 
separately  as  series  II.  The  roughness  of  the  remaining  stocks  and 
also  of  the  fanciers'  "Peruvians"  and  " Abyssinians"  we  may  call 
series  I.  In  series  I  all  the  variations  found  may  be  arranged  with  con- 
siderable accuracy  in  a  single  linear  series.  Thus  Castle  (1905)  used 
six  grades,  passing  from  rough  A  with  the  maximum  number  of  rosettes 
to  rough  F,  smooth  except  for  the  hind  toes.  These  grades  will  be 
used  in  this  discussion,  with  the  exception  that  it  has  been  found  con- 
venient to  combine  grades  C  and  D,  leaving  five  grades,  A  to  E.  These 
letters  used  for  grades  must  not  be  confused  with  those  used  to  name 
the  rosettes. 


102 


INHERITANCE    IN   GUINEA-PIGS. 


Reversal  of  hair  direction  on  the  hind  toes  is  the  most  constant 
feature  of  the  roughness  of  series  I  and  has  been  found  in  all  rough 
guinea-pigs  of  series  I  without  exception.  Following  is  the  usual  order 
of  succession  of  the  additional  rosettes  and  irregularities  found  in  pass- 
ing from  a  smooth  to  a  full-rough: 


Hind  toes K 

Front  toes J 

Dorsal  crest e 

Side  rosettes,  crest  between  ears E,C 


Forehead,  hip,  ventral  rosettes. . .   A,F,H,I,L 

Eye  rosettes B 

Groin,  shoulder,  second  side  ro- 
settes    G,D,E2 


There  is  seldom  more  than  a  slight  amount  of  asymmetry.  As  a 
rule  the  paired  rosettes  are  present  or  absent  as  pairs.  The  most 
common  exception  is  in  the  side  rosettes  in  low-grade  partial-roughs. 
Among  these  it  is  not  uncommon  to  find  a  good  rosette  on  one  side  and 
merely  a  slight  change  in  hair  direction  on  the  other.  In  classifying, 
six  of  the  most  distinct  sets  of  rosettes  have  been  used  as  the  principal 
criteria,  viz,  forehead,  eyes,  sides,  hips,  front  toes,  and  hind  toes. 


CLASSIFICATION. 

Rough  A. — The  forehead  and  five  critical  pairs  of  rosettes  must  be 
well  developed.  In  addition,  there  is  always  some  ventral  roughness 
and  a  crest  between  the  ears. 

Rough  B. — This  includes  various  conditions  intermediate  between 
rough  A  and  rough  C. 

Rough  C. — There  is  only  one  pair  (or  half  pair)  of  well-developed 
rosettes,  usually  the  side  rosettes.  There  is  always,  in  addition,  rough- 
ness on  at  least  the  hind  toes  and  usually  a  crest  between  the  ears. 

Rough  D. — A  mid-dorsal  crest  is  present  and  roughness  of  at  least 
the  hind  toes,  but  no  well-marked  rosettes. 

Rough  E. — Roughness  is  confined  exclusively  to  the  toes,  usually  to 
the  hind  toes. 

The  following  list  shows  the  variations  which  have  been  met  with  in 
each  grade;  the  letters  represent  the  rosettes: 

Rough  A.  ABcEFHIJK  to  ABCDEiE2FGHIJKL. 

Rough  B.  AcEJK,  AcEHJK,  abFGJK,  ABcFHIJKl,  ABcDEHIJKl. 

Rough  C.  EK,  EJK,  cEK,  cEJK. 

Rough  D.  eK,  cK,  eJK,  cJK. 

Rough  E.  K,  JK. 

PREVIOUS  WORK. 

Nehring  (1894)  made  crosses  between  rough  guinea-pigs  and  the 
wild  species  Cavia  aperea.  He  described  the  young  as  smooth,  but 
noted  that  a  mane  developed  along  the  middle  line  of  the  back.  Castle 
(1905)  demonstrated  that  rough  fur  behaves  as  a  Mendelian  unit 


ROUGH   FUR.  103 

character,  dominant  over  smooth,  and  is  thus  an  example  of  the  com- 
paratively rare  class  of  dominant  mutations.  He  found  that  the  grade 
of  roughness,  while  fairly  constant  in  some  stocks,  could  be  reduced  by 
crossing  with  smooth  guinea-pigs  of  a  particular  stock  (tricolor),  which 
he  described  as  prepotent  smooth.  Detlefsen  (1914)  found  that  rough 
fur  in  hybrids  between  rough  guinea-pigs  and  the  wild  species  Cavia 
rufescens  continued  to  be  inherited  in  Mendelian  fashion,  but  that  domi- 
nance ceased  to  be  complete.  The  writer  began  experiments  in  1913  at 
Professor  Castle's  suggestion,  to  investigate  further  the  heredity  of 
variations  in  the  rough  character. 

MATERIAL. 

Several  stocks  have  been  used  as  material: 

(1)  J^-toe  stock. — A  full-rough  was  crossed  with  members  of  the  4-toe 
stock,  and  by  repeated  back-crosses  into  the  latter  a  stock  has  been 
produced  which  is  practically  pure  4-toe.     No  partial-roughs  have  ever 
appeared  in  these  crosses.    Pure  4-toe  smooth  animals  have  been  very 
useful  in  the  experiments,  since  it  has  been  amply  proved  that  when 
crossed  with  full-roughs  they  never  reduce  the  grade  of  rough. 

(2)  Tricolor  stock. — Most  of  the  partial-roughs  experimented  with  are 
of  very  mongrel  stock,  with,  however,  more  or  less  tricolor  ancestry. 
In  this  section  on  rough  fur  the  term  tricolor  stock  will  be  used  for 
convenience  for  these  animals,  without  implying  that  all  of  them 
actually  were  tricolors. 

(3)  Lima  stock. — This  stock  as  has  been  described  was  derived  en- 
tirely from  8  guinea-pigs  (2  nearly  full-rough  (rough  B)  and  6  smooth) 
brought  from  Peru  in  1913. 

(4)  Rufescens  hybrids. — The  writer  has  worked  with  a  few  rough 
animals  descended  from  Detlefsen's  hybrids  and  containing  from  I  to 
TTX  Cavia  rufescens  ancestry. 

(5)  Cutleri  hybrids. — Crossing  with  Cavia  cutleri  has  been  found  by 
the  writer  to  have  a  similar  effect  on  the  rough  character  to  that 
described  by  Nehring  (1894)  for  C.  aperea  and  by  Detlefsen  (1914)  for 
C.  rufescens.     The  behavior  of  the  roughness  in  these  cutleri  hybrids 
has  been  investigated. 

(6)  Miscellaneous  smooth  guinea-pig  stocks  have  been  used  in  some 
of  the  experiments.     All  used  resemble  the  4-toe  smooths  in  giving  no 
partial-roughs  when  crossed  with  full-roughs. 

(7)  BW,  lea,  and  Arequipa  stock  occasionally  have  shown  a  slight 
roughness  which  is  distinct  from  the  usual  type  and  is  discussed  later 
under  series  II.     The  BW  stock  has  been  used  in  a  few  cases  as  a 
source  of  smooth  guinea-pigs.     Aside  from  the  slight  roughness  of 
series  II  all  of  those  used  have  behaved  like  4-toe  smooths.     Smooth 


104 


INHERITANCE    IN    GUINEA-PIGS. 


4  toe 
stock 


leas,  on  the  other  hand,  behaved  like  the  wild  cavies  in  reducing  the 
roughness. 

PROBLEMS. 

The  following  figures  show  the  kinds  of  roughs  which  have  appeared 
in  the  experiments  with  the  four  principal  stocks  and  the  nature  of 
the  variability  in  the  rough  character,  the  inheritance  of  which  it  is 
desired  to  analyze.  All  roughs  are  included,  but  only  such  smooths 
as  had  at  least  one  rough  parent. 

Inspection  of  figure  7  at  once  shows  striking  differences  in  the 
variability  of  the  rough  character  in  the  different  stocks.  In  the  4-toe 
stock  there  is  a  wide  gap  between  the  lowest  rough  and  the  smooths 
which  come  from  the  same  parents.  Only  one  individual  in  the  4-toe 

stock  was  graded  rough  B  and  this 

A  CDC  Sm 

was  close  to  rough  A  (lacked  only 
groin  and  hip  rosettes).  Most  of 
the  individuals  were  strong  rough 
A.  In  the  Luna  stock  most  of 
the  individuals  which  were  rough 
at  all  were  rough  B  or  a  weak 
rough  A,  but  5  were  rough  C  or  D. 
Among  the  tricolor  and  cutleri 
hybrids  a  continuous  series  can 
be  formed  passing  from  the  best 
roughs  to  the  smooths.  Both 
show  a  distinctly  bimodal  distri- 
bution of  the  roughs,  the  modes 
being  at  rough  A  and  rough  C. 
Such  a  distribution  would  of 
course  be  purely  artificial  if  rough 
B  were  a  more  limited  category 
than  rough  A  or  rough  C,  but  the 

FIG.  7. — Distribution  of  grades  of  roughness  of  the    definitions  show  that  TOUgh  B  in- 
fur  in  four  stocks  of  guinea-pigs.  ^^   perhaps  the  ^^   range 

of  possible  variation.  Further,  the  large  number  of  rough  B's  in  the 
Lima  stock  shows  that  this  class  may  be  practically  as  numerous  as 
rough  A  under  the  right  hereditary  conditions.  Thus  there  are  strong 
intimations  that  in  the  tricolor  and  cutleri  stocks,  rough  A  and  rough 
C  differ  by  a  unit  hereditary  difference. 

The  problem  of  the  inheritance  of  the  variations  in  the  rough  char- 
acter thus  seems  to  resolve  itself  into  three  phases:  (1)  The  inheritance 
of  roughness  of  any  sort  as  opposed  to  smoothness;  (2)  the  inheritance 
of  a  more  or  less  full-rough  type  averaging  about  rough  A  as  opposed 
to  a  partial-rough  type  averaging  between  rough  C  and  D;  (3)  the 
inheritance  of  the  variations  within  the  full-rough  and  partial-rough 
types. 


Tricolor 
stock 


Lima 
stock 


Cutleri 
hybrids 


ROUGH   FUR. 


105 


INHERITANCE  OF  ROUGH  AS  OPPOSED  TO  SMOOTH. 

Castle  (1905)  demonstrated  that  all  roughs  differ  from  smooths  by  a 
Mendelian  unit-factor  and  that  rough  is  dominant  over  smooth.  The 
writer's  experience  fully  confirms  this  conclusion. 

In  nearly  3,000  young  recorded,  smooth  by  smooth  has  never  given 
rise  to  rough  (of  series  I)  in  spite  of  much  rough  ancestry,  with  one 
possible  exception.  This  exception  was  of  a  kind  which  was  expected 
and  was  being  tested  for  when  found.  One  of  the  smooth  parents  was 
undoubtedly  like  rough  E  genetically.  The  case  will  be  discussed  later. 

TABLE  45. 


Rough  X  rough. 

Rough  X  smooth. 

Formula  and  stock. 

Rough. 

Smooth. 

Formula  and  stock. 

Rough. 

Smooth. 

RR  X  Rr: 
4003  (tri)  

6 

10 

88 
18 
17 

0 

3 

28 
7 
2 

RR  X  rr: 
4003  (tri)  

11 

29 
104 
56 
60 
54 

0 

32 
125 
55 
63 

48 

Rr  X  Rr: 

4-toe  

Rr  X  rr: 
4-toe  

Tricolor  

Tricolor  

Tjima  ,....,     ...... 

Lima  

Cutleri  hybrid  

Cutleri  hybrid  

Total  

Miscellaneous 

Total     . 

133 

(130) 

40 

(43) 

303 
(313) 

323 
(313) 

Expectation 

Expectation 

Largely  Rr  X  Rr: 
Miscellaneous  

Largely  Rr  X  rr  

46 

12 

16 

12 

On  the  other  hand,  rough  by  rough  has  often  given  smooth.  In  the 
cross  of  rough  by  smooths  from  stocks  in  which  roughs  have  never 
occurred,  all  or  half  of  the  young  are  rough.  All  wild  cavies,  for  ex- 
ample, are  smooth  and  have  only  smooth  descendants  when  crossed 
with  smooth  guinea-pigs.  They  have  numerous  rough  young  in  Fx  when 
crossed  with  rough  guinea-pigs.  Thus  it  is  clear  that  rough  is  domi- 
nant. Table  45  is  a  summary  of  the  rough  crosses  made  by  the  writer. 
Grades  of  roughness  are  ignored.  No  special  attempt  has  been  made 
to  obtain  homozygous  roughs.  Male  4003,  rough  E,  is  the  only  one 
which  has  been  adequately  proved  homozygous.  Male  R197,  rough 
A  (cross  46),  is  another  which  is  probably  homozygous.  In  the  cross 
Rr  X  Rr  above,  only  matings  are  included  in  which  both  animals  are 
known  to  be  heterozygous,  either  because  of  a  smooth  parent,  or, 
having  had  12  or  more  young,  because  of  smooth  young.  Tabulated  in 
this  way,  the  expectation  is  not  appreciably  different  from  3  rough  to 
1  smooth.  Other  litters  of  rough  by  rough  are  tabulated  above. 
Probably  most  of  these  are  of  the  type  Rr  X  Rr,  although  in  some  cases 
there  were  no  smooth  young.  In  crosses  Rr  X  rr,  the  only  cases  tab- 


106 


INHERITANCE   IN   GUINEA-PIGS. 


ulated  are  those  in  which  the  rough  is  known  to  be  Rr  because  of 
a  smooth  parent,  or  because  of  a  smooth  young  one  in  6  or  more. 
Expectation  is  here  1  to  1.  The  remaining  cases  of  rough  by  smooth, 
in  which  expectation  is  still  probably  not  far  from  1  to  1,  are  also 
given. 

These  results  are  in  harmony  with  the  view  that  rough  differs  from 
smooth  by  a  dominant  unit  factor. 

INHERITANCE  OF  MAJOR  VARIATIONS. 

Before  giving  any  hypotheses,  it  will  be  well  to  present  the  experi- 
mental results  with  the  immediate  deductions  which  can  be  drawn 
from  them  (tables  46  to  55) . 

(1)  In  some  stocks  there  is  very  little  variation  in  the  rough  char- 
acter and  there  is  a  wide  gap  between  the  lowest  rough  and  smooth. 
The  4-toe  stock  is  an  excellent  example  of  such  a  stock.  It  is  worthy 
of  note  that  we  get  a  similar  result  hi  the  Lima  stock  if  we  exclude  the 
litters  of  L6,  L24,  L56,  and  L99.  Female  L6,  smooth,  was  one  of  the 
original  8  in  the  Lima  stock.  Female  L24,  smooth,  was  her  daughter. 
Female  L56,  rough  C,  was  the  daughter  of  L24,  and  male  L99,  rough  C, 
was  the  son  of  L56.  Most  of  the  tame  guinea-pig  stocks  (BW,  dilute 
selection)  seemed  to  be  like  the  4-toe  stock  in  the  above  respect  when- 
ever rough  was  introduced  into  them  in  a  cross. 

TABLE  46. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(45) 

Four-toe  stock: 
A  X  A  

10 

3 

(49) 

A  X  Sm   

28 

1 

32 

(58) 

Lima  stock,  except  L6,  L24,  L56, 
and  L99: 
B  X  B   .      .      . 

7 

5 

3 

(59) 

A  X  Sm  

21 

5 

17 

(60) 

B  X  Sm  

5 

9 

21 

(63) 
(65,  66) 

Miscellaneous  stock: 
A,  B  (Lima)  X  Sm  (4-toe)  .  . 
A  X  Sm  

4 
31 

4 
1 

4 
36 

Most  of  those  graded  rough  A  or  rough  B  above  must  be  heterozy- 
gous. As  nothing  higher  than  rough  A  appeared  in  the  crosses  A  X  A 
and  B  X  B,  it  seems  clear  that  the  homozygotes  in  these  stocks  at 
least  are  no  more  rough  than  the  heterozygotes,  i.  e.,  dominance  is 
complete. 

(2)  When  a  wild  species  of  Cavia  (smooth),  or  a  smooth  of  certain 
tame  stocks  is  crossed  with  a  full-rough,  the  rough  young  are  of  low 
grade — rough  C  or  D. 


ROUGH   FUR. 


107 


As  has  been  mentioned  before,  Nehring  (1894)  crossed  a  rough  male 
guinea-pig  with  Cavia  aperea  of  Argentina.  He  described  the  young  as 
smooth  at  first,  but  developing  a  mane  along  the  back  later.  This 
was  evidently  the  dorsal  crest  of  rough  D.  The  reversal  of  hair  direc- 
tion on  the  hind  toes  might  easily  have  been  overlooked.  Detlefsen 
(1914)  described  crosses  of  C.  rufescens  of  Brazil  with  full-rough  guinea- 
pigs.  His  rufescens  was  undoubtedly  a  different  species  from  the  aperea 
used  by  Nehring,  since  the  latter  found  complete  fertility  among  the 
hybrids  of  both  sexes,  whereas  Detlefsen  found  sterility  among  all  the 
male  hybrids.  The  rough  young  were  rough  D.  The  skin  of  one  of 
them  (A10)  shows  roughness  on  all  the  toes  and  a  very  slight  dorsal 
crest.  The  writer  has  crossed  rough  A  guinea-pigs  with  C.  cutleri  of 
Peru  with  similar  results.  Nine  rough  young  have  been  obtained,  of 
which  3  show  good  side  rosettes  and  are  rough  C,  while  the  others 
merely  show  a  dorsal  crest  (and  rough  toes)  and  are  rough  D.  A  male 
of  pure  lea  stock,  which  being  from  feral  stock  probably  had  consider- 
able wild  ancestry,  was  tested  by  crosses  with  full  roughs  and  also 
gave  only  partial-roughs — 5  all  rough  C.  Castle  (1905)  obtained 
partial-roughs,  C  or  D,  on  crossing  full-roughs  with  smooths  of  tri- 
color stock.  The  writer  has  made  further  crosses  of  this  kind  with 
similar  results.  One  smooth  guinea-pig  of  the  Lima  stock,  L24,  had 
some  partial-rough  young  when  crossed  with  full-roughs  of  her  stock. 

TABLE  47. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

Smooth,  of  wild  or  feral  stock  : 
A  X  Sm  (C.  aperia)  

1 

Nehring  (1894). 

(68) 
(67) 

A  X  Sm  (C.  rufescens)  
A  X  Sm  (C.  cutleri)  
A  X  Sm  (lea)  

3 
5 

4 
6 

7 
15 
4 

Detlefsen  (1914). 

(71,  74) 
(65) 
(59,  60) 

Certain  tame  stocks  and  wild 
hybrids  : 
A  X  Sm  (|  cutleri)  
A  X  Sm  (?,  5*5  rufescens)  . 
A  X  Sm  (L6,  L24)  

10 
1 

4 

3 
1 
1 

10 
2 
3 

1 

23 
6 

(51) 

A  X  Sm  (Tricolor)  

6 

3 

3 

19 

The  results  given  in  table  47  show  that  in  partial-roughs  from  a  great 
variety  of  sources,  the  low  grade  of  the  roughness  is  not  due  to  a  vari- 
ation of  the  rough  factor, i.e.,  to  an  allelomorph, nor  is  it  due  to  an  inde- 
pendent duplicate  rough  factor  which  produces  somewhat  similar 
effects  to  the  factor  of  full-roughs.  These  partial-roughs  have  the 
identical  rough  factor  present  in  full-roughs  derived  directly  from  the 
latter. 

(3)  When  a  wild  cavy  is  crossed  with  a  partial-rough  guinea-pig, 
rough  young  of  the  lowest  grade  (rough  E)  are  produced. 


108 


INHERITANCE   IN    GUINEA-PIGS. 


No  rough  E  young  were  produced  in  the  crosses  under  (2)  where 
one  parent  was  full-rough. 


TABLE  48. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(69) 

C,  D  X  Sm  (C.  cutleri)  

1 

1 

9 

12 

(4)  Partial-roughs  crossed  together  may  give  all  grades  of  roughness 
from  full-rough  (A)  to  the  lowest  partial-rough  (E) . 


TABLE  49. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(76) 

cutleri  hybrids: 
C  X  C  

1 

3 

1 

(52) 

Tricolor  : 
C,  D  X  C  

18 

6 

19 

7 

12 

17 

(53) 

C,  D  X  E  

4 

1 

6 

1 

(55) 

E  X  E  

4 

3 

(5)  Full-roughs  crossed  together  have  never  given  partial-roughs. 
Crosses  in  the  4-toe  and  Luna  stock  have  already  been  given.  Below 
are  crosses  of  rough  A  by  rough  A  in  the  tricolor  and  cutleri  stocks  in 
which  each  rough  A  parent  had  one  or  both  of  its  parents  partial- 
rough  (C,  D)  or  in  the  case  of  the  cutleri  hybrids,  an  FI  hybrid. 


TABLE  50. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(46) 

Tricolor  A  X  A  

17 

2 

7 

(75) 

J  cutleri  A  X  A  

3 

(6)  Full-roughs,  one  or  both  of  whose  parents  were  partial-roughs, 
have  given  no  partial-rough  young  in  crossing  with  smooths  of  4-toe 
stock. 

TABLE  51. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(50) 

A  (Tri)       X  Sm  (4-toe)  .... 

19 

20 

(73) 

A  (J  cut)  X  Sm  (4-toe)  

2 

2 

In  (73)  two  of  the  |  cutleri  rough  A  did  not  come  from  a  partial-rough 
parent,  but  from  smooth  \  cutleri  hybrids. 


ROUGH    FUR. 


109 


(7)  Partial-roughs  crossed  with  smooths  of  4-toe  or  a  similar  stock 
give  partial-rough  young,  and  also,  in  most  cases,  full-rough  and 
smooth  young. 

TABLE  52. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(54) 

C,  D  (Tri)  X  Sm  (4-toe,  etc.)  

34 

?9 

13 

1 

79 

(64) 
(72) 
(61) 

C  (i,  j,  fa  rufescens)  X  Sm  (4-toe,  etc.)  .  . 
C,  D  (j,  J  cutleri)  X  Sm  (4-toe,  etc.)  .... 
L  56  C  X  Sm  (Lima)  

3 
12 

? 

1 

2 
6 
1 

6 

5 
21 
2 

(56) 

E  (Tri)  X  Sm  (4-toe)  

13 

8 

Crosses  (3)  to  (7)  show  that  full-rough  can  be  recovered  from  partial- 
rough  usually  without  trouble,  but  that  partial-rough  can  not  be  re- 
covered from  full-rough,  either  in  crossing  full-roughs  together  or  with 
ordinary  smooth  guinea-pigs  (4-toe,  etc.).  Cross  (7)  is  more  significant 
than  appears  at  first  sight.  We  know  that  4-toe  smooths  transmit 
nothing  which  can  reduce  the  grade  of  roughness.  Thus,  when  we 
find  partial-rough  by  4-toe  smooth  giving  partial-rough  young,  we  see 
that  the  rough  factor  and  the  factor  or  factors  responsible  for  the  low 
grade  of  roughness  can  be  transmitted  in  the  same  gamete. 

(8)  Most  partial-roughs  crossed  with  full-roughs  give  a  very  similar 
result  to  the  cross  partial-rough  by  4-toe  smooth,  except  that  fewer 
smooths  are  produced. 

TABLE  53. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(47) 

A                      X  C  (Tri)  

10 

1 

5 

1 

10 

(58) 

B  (Lima)          X  C  (Lima) 

1 

1 

(70) 

A  (4-toe,  etc.)  X  C,  D  (},  i  cutleri)  

8 

3 

8 

?, 

?, 

4 

(48) 

A  (Tri)             X  E  (Tri)  

a 

1 

(9)  The  lowest  grade  of  roughs  (E)  very  rarely  have  either  a  full- 
rough  parent  or  full-rough  young.  They  also  very  rarely  have  a 
smooth  parent  of  such  a  stock  as  4-toe. 

Of  the  rough  young,  507  have  been  recorded  (excluding  8  from  mixed 
bimaternal  litters) ;  413  of  these  had  a  full-rough  (A,  B)  or  a  4-toe 
smooth  parent;  yet  these  include  only  3  rough  E  young.  On  the  other 
hand,  13  rough  E  are  included  in  the  67  rough  young  from  C  or  D  X  C ; 
6  are  included  in  the  11  from  C  or  D  X  E,  9  are  included  in  the  11 
rough  young  from  C  X  smooth  Cavia  cutleri  and  all  of  the  4  rough 
young  from  E  X  E  were  rough  E.  Table  54  shows  the  matings  in 
which  one  or  both  of  the  parents  were  rough  E.  These  are  repeated 
from  other  crosses. 


110 


INHERITANCE   IN   GUINEA-PIGS. 


The  offspring  of  male  4003  rough  E  are  of  special  interest.  He  was 
undoubtedly  homozygous  rough;  the  chance  that  he  was  heterozygous 
is  (£)n(f)6  =  0.0001.  As  he  was  the  lowest  grade  of  rough,  he  very 
emphatically  disproves  any  necessary  relation  between  homozygosis 
and  high  development  of  the  rough  character,  or  between  heterozygosis 
and  partial  roughness. 

TABLE  54. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

8m 

(56) 

E  X  Sm  (4-toe)  

13 

8 

(48) 

E  X  A  

?, 

1 

(53) 

E  X  C,  D  

4 

1 

6 

1 

(55) 

E  X  E  

4 

3 

(10)  Occasionally  a  smooth  from  a  cross  which  produces  rough  E 
will  transmit  the  rough  factor,  breeding  like  a  rough  E.  Rough  E 
grades  into  smooth.  From  a  cross  which  can  produce  rough  E,  8  smooth 
animals  were  tested  by  crossing  with  4-toe  smooths  to  determine 
whether  a  smooth  can  ever  be  like  rough  E  genetically.  One  such 
animal,  female  R201,  was  found. 

TABLE  55. 


Cross. 

Stock  and  grade. 

A 

B 

C 

D 

E 

Sm 

(57) 

7  Sm  (C  X  C)           X  Sm  (4-toe)  .  .  . 

32 

R  201  Sm  (C  X  C)  X  Sm  (4-toe)  .  .  . 

1 

1 

The  case  is  not  quite  as  clear  as  could  be  desired,  since  R201  seemed 
to  show  a  trace  of  irregularity  on  one  hind  toe  when  first  graded.  As 
an  adult  she  is  indistinguishable  from  a  smooth. 

These  experiments  are  sufficient,  it  is  believed,  to  establish  the  mode 
of  inheritance  of  the  major  variations  of  the  rough  character. 

First,  it  is  clear  that  partial-roughs  do  not  owe  then*  roughness  to  an 
allelomorph  of  the  rough  factor  or  to  an  independent  duplicate  rough 
factor,  but  to  the  same  factor  found  in  full-roughs.  Reasons  were 
given  under  (2). 

Next,  any  hypothesis  is  untenable  according  to  which  partial-roughs 
are  due  to  imperfect  dominance  and  hence  are  necessarily  heterozygous 
either  with  the  ordinary  smooth  factor  of  guinea-pigs  or  with  a  more 
potent  allelomorph  of  the  latter  present  in  wild  cavies  and  special  stocks 
of  tame  guinea-pigs.  The  latter  hypothesis  was  suggested  by  Det- 
lefsen  (1914),  in  the  case  of  the  partial-roughs  among  the  rufescens 
hybrids.  He  represented  the  rough  factor  by  Rf ,  the  ordinary  smooth 
factor  by  rf ,  and  the  smooth  factor  of  Cavia  rufescens  by  rf '.  He  sup- 
posed that  Rf  is  completely  dominant  over  rf ,  but  incompletely  domi- 
nant over  rf'.  Thus  Rfrf  would  be  a  full-rough,  but  Rfrf'  a  partia- 


ROUGH   FUR.  Ill 

rough.  This  hypothesis  explains  very  satisfactorily  all  of  the  crosses 
given  except  those  under  (7),  repeated  under  (9)  and  (10).  It  can  not 
explain  the  case  of  male  4003  rough  E,  who  was  undoubtedly  homo- 
zygous  for  the  rough  factor  (RfRf)  and  yet  was  the  lowest  grade  of 
partial-rough.  Further,  it  can  not  explain  the  occurrence  of  partial- 
rough  young  coming  from  the  cross  partial-rough  by  4-toe  smooth. 
The  latter  are  necessarily  rfrf  under  the  above  hypothesis. 

Rfrf'  X  rfrf  -  Rfrf  +  rfrf'. 

Rough  C,  D,  E  X  smooth  =  rough  A  +  smooth. 

Under  this  hypothesis,  the  rough  factor  Rf  and  the  factor  which 
reduces  the  grade  of  rough  rf '  can  not  be  present  in  the  same  gamete. 
But  this  cross  actually  gave  70  partial-rough  young,  56  from  tricolor 
partial-roughs,  12  from  partial-rough  cutleri  hybrids,  and  at  least  1, 
probably  2,  where  the  partial-rough  parent  owed  its  low  grade  to  Cavia 
rufescens.  Female  A606  rough  C  was  \  rufescens.  Her  parents  were 
2193,  a  full-rough  guinea-pig,  and  A63,  a  smooth  rufescens  hybrid. 
The  hypothetical  factor  rf  could  only  have  come  from  the  latter. 
The  parents  of  A63  were  A55,  a  pure  Cavia  rufescens,  and  9586  of 
BW  stock,  a  stock  which  has  shown  no  tendency  to  reduce  the  grade 
of  full-roughs  on  crossing  with  them.  It  thus  seems  clear  that  A606 
owes  her  low  grade  of  rough  to  her  Cavia  rufescens  grandfather.  She 
was  crossed  with  a  4-toe  smooth  male,  166,  and  had  two  rough  young, 
whose  grades  unfortunately  were  not  recorded  at  birth.  One,  however, 
A1687,  is  still  living  (August  1915),  and  is  a  typical  rough  C.  There  is 
reason  for  believing  the  other  to  have  been  of  the  same  grade.  Thus  in 
tricolors,  Cavia  cutleri  and  Cavia  rufescens  hybrids,  the  same  gamete  can 
transmit  the  rough  factor  and  the  factor  or  factors  which  limit  the  full 
development  of  the  rough  character.  The  formula  Rfrf'  can  not, 
therefore,  be  used  for  partial-roughs. 

There  remains  only  one  line  of  explanation.  Partial-roughs  must 
differ  from  full-roughs  by  possessing  an  independently  inherited  modi- 
fying factor  (or  factors).  An  incompletely  dominant  unit  modifying 
factor  will  explain  all  of  the  results  satisfactorily.  Let  us  represent  the 
wild  condition  (aperea,  rufescens,  cutleri)  by  rrSS.  Let  us  suppose  that 
the  dominant  mutation  R  is  necessary  for  any  roughness  [of  series  I] 
and  produces  with  rare  exceptions  at  least  reversal  of  hair  direction 
on  the  hind  toes  (rough  E).  The  second  mutation,  s,  when  heterozy- 
gous, may  permit  roughness  to  extend  to  grades  D  or  C ;  when  homozy- 
gous  it  permits  roughness  to  reach  grades  B  or  A. 

rrSS  smooth Wild  species,  lea  stock. 

rrSs  smooth Most  tricolor  smooths. 

rrss  smooth 4-toe,  BW,  BB,  dilute  stock,  most  Lima  smooths. 

RrSS  rough  E  (rarely  smooth) R  140,  etc. 

RRSS  rough  E  (rarely  smooth) 4003. 

RrSs  rough  C  or  D  (rarely  E  or  B) .  .  .   Most  tricolor  partial-roughs. 
RRSs  rough  C  or  D. 

RrSS  rough  A  (less  frequently  B) .  .  . .   4-toe,  most  Lima  roughs. 
RRss  rough  A. 


112  INHERITANCE   IN   GUINEA-PIGS. 

This  explanation  fits  very  well  the  results  which  have  been  given 
qualitatively.  As  the  numbers  are  rather  small,  and  as  it  is  necessary 
besides  to  assume  some  overlapping  of  class  ranges,  much  emphasis 
can  not  be  laid  on  the  quantitative  results.  Nevertheless,  the  fit  is 
in  all  cases  reasonably  close.  Let  us  take  up  the  qualitative  results  in 
order. 

(1)  In  some  stocks  there  is  very  little  variation  in  the  rough  char- 
acter and  there  is  a  wide  gap  between  the  lowest  rough  and  smooth. 
Evidently  if  the  4-toe  and  similar  stocks  are  pure  for  factor  s,  only 
full-roughs  and  smooths  can  appear  (RRss,  Rrss,  rrss).    Apparently 
7  of  the  original  8  in  the  Lima  stock  were  ss,  while  one,  L6,  was  rrSs. 

(2)  When  a  wild  species  of  cavy  (smooth)  or  a  smooth  of  certain  tame 
stocks  is  crossed  with  a  full-rough,  the  rough  young  are  of  low  grade, 
rough  C  or  D.    This  result  necessarily  follows  from  a  cross  of  the  type 
rrSS  (wild,  lea,  tricolor)  by  Rrss  (rough  A).     The  rough  young  RrSs 
should  be  rough  C  or  D. 

(3)  When  a  wild  cavy  is  crossed  with  a  partial-rough  guinea-pig, 
rough  young  of  the  lowest  grade,  rough  E,  are  produced. 

rrSS  X  RrSs  =  RrSs  +  RrSS  +  2rr 
Sm         C  C  E  2Sm 

(4)  Partial-roughs  crossed  together  may  give  all  grades  of  roughness 
from  full-rough  (A)  to  the  lowest  partial-rough  (E).     Most  of  the 
partial-roughs  handled  should  be  RrSs. 

RrSs  X  RrSs  =  3  Rss  +  6  RSs  +  3  RSS  +  4  rr 
C  C  3A          6  C,  D     3  E  4Sm 

(5)  Full-roughs  crossed  together  have  never  given  partial-roughs. 
A  full-rough,  whatever  its  parentage,  must  be  RRss  or  Rrss.    There  is 
no  way  in  which  factor  S,  necessary  for  partial-roughs,  can  be  trans- 
mitted by  full-roughs. 

(6)  Full-roughs,  one  or  both  of  whose  parents  were  partial-roughs, 
have  given  no  partial-rough  young  on  crossing  with  smooths  of  4-toe 
stock.     Smooths  of  4-toe  stock  are  all  necessarily  rrss  and  can  not 
transmit  factor  S. 

(7)  Partial-roughs  crossed  with  smooths  of  4-toe  or  a  similar  stock 
give  partial-rough  young  and  also,  in  most  cases,  full-rough  and  smooth 
young. 

RrSs  X  rrss  =  Rrss  +  RrSs  +  2  rr 

C  Sm  (4-toe)       A  C  2  Sm 

(8)  Most  partial-roughs  crossed  with  full-roughs^give  a  very  similar 
result  to  the  cross  partial-rough  by  4-toe  smooth,*  except  that  fewer 
smooths  are  produced. 

RrSs  X  Rrss  =  3  Rss  +  3  RSs  +  2  rr 
C  A  3A          3C  2Sm 

(9)  The  lowest  grade  of  roughs  (E)  very  rarely  have^  either  a  full- 
rough  parent  or  full-rough  young.     They  also  very  rarely  have  a 


ROUGH   FUR. 


113 


smooth  parent  of  such  a  stock  as  4-toe.  The  parents  and  offspring  of 
rough  E  (SS)  must  necessarily  have  at  least  one  S  (SS  or  Ss),  while 
full-roughs  and  4-toe  smooths  are  ss.  The  three  exceptional  rough  E's 
can  only  be  interpreted  as  extreme  minus  fluctuations  of  type  RrSs. 

(10)  Occasionally  a  smooth  from  a  cross  which  produces  rough  E  will 
transmit  the  rough  factor,  breeding  like  a  rough  E.  The  discovery  of  a 
smooth  (RrSS)  which  had  a  rough  C  young  one  (RrSs)  when  crossed 
with  a  4-toe  smooth  (rrss),  apparently  violating  the  dominance  of 
roughness,  is  the  kind  of  exception  that  proves  the  rule,  coming  as  it 
did  where  predicted. 

The  descendants  of  male  4003  illustrate  the  theory  very  well.  He 
was  of  constitution  RRSS  by  theory. 

TABLE  56. 


A 

B 

C 

D 

E 

3m 

P! 

RRSS  X  rrss   

4003 

4-toe 

Fi 

RrSs   .              

11 

F2 

7  Rss    +  13  RSs  +  7  RSS  +  9  rr.  .  . 

8 

5 

8 

3 

5 

7 

7  A,  B       13  C,  D      7  E            9  Sm 

Of  those  called  rough  B,  2  were  close  to  rough  A  and  3  were  close  to 
rough  C. 

POSSIBILITIES  OF  LINKAGE  AMONG  ROUGH  AND  COLOR  FACTORS. 

In  the  mating  just  cited,  factors  R  and  S  enter  the  cross  from  the 
same  individual.  The  excess  of  full-roughs  (Rss),  probably  10  where 
7  are  expected,  makes  any  linkage  between  R  and  S  very  unlikely. 
Another  test  is  furnished  by  the  cross  of  double  heterozygotes,  RrSs 
with  4-toe  smooths,  rrss,  where  it  is  definitely  known  whether  R  and  S 
enter  the  cross  together  or  apart.  Cases  which  should  show  coupling 
if  there  is  linkage  are  cross  54-1,  2,  4,  5,  6,  12,  15,  16,  17,  and  cross 
72-5,  6,  7.  Cases  which  should  show  repulsion  are  cross  61-1,  cross 
64-1,  3,  and  cross  72-1,  2,  8,  9,  10. 

TABLE  57. 


A,B 

C,  D 

Sm 

Cross- 

Link- 

Rsrs. 

RSrs. 

rr  — 

overs. 

ages. 

C,  D        Sm 

Coupling  —  RSrs    X  rsrs  

26 

29 

60 

26 

29 

Repulsion  —  RsrS  X  rsrs  

14 

6 

16 

6 

14 

32 

43 

The  indication  of  linkage  is  too  slight  to  be  considered  significant, 
especially  in  view  of  the  excess  of  cross-overs  hi  the  F2  data. 

Thus  there  is  probably  no  linkage  between  R  and  S.  It  is  interesting 
to  analyze  the  data  with  regard  to  possible  linkages  of  these  factors  with 


114 


INHERITANCE   IN   GUINEA-PIGS. 


any  of  the  5  known  sets  of  color  factors.  Four  of  the  sets  of  color 
factors,  those  in  which  non-agouti  (a),  yellow  (e),  brown  (b),  and 
albinism  (Ca)  are  the  lowest  recessives,  are  known  to  be  independent  of 
each  other  (Part  I).  As  regards  the  pink-eye  factor  (p),  it  is  merely 
known  that  cross-overs  occur  between  it  and  non-agouti,  albinism, 
and  yellow,  and  that  it  is  not  an  allelomorph  of  brown  (i.  e.,  pink-eye 
X  brown  gives  black-eyed  intense  young). 

Data  on  the  possible  repulsion  of  R  and  A  are  furnished  by  cross  72- 
1,  2,  5,  6,  8,  9,  10  and  cross  64-1.  Coupling  data  are  to  be  found  in 
64-3  and  66-1,  3. 

TABLE  58. 


Ag-Rf 
ARar 

Ag-Sm 
Arar 

B-Rf 

allar 

B-Sm 
arar 

Cross- 
overs. 

Link- 
ages. 

Ag-Rf      B-Sm 
Coupling  —  ARar   X    arar  

4 

7 

11 

3 

18 

7 

Repulsion  —  AraR  X    arar  

7 

5 

7 

9 

16 

12 

34 

19 

There  is  an  excess  of  cross-overs.  The  most  probable  interpretation 
is  that  there  is  no  linkage. 

Data  on  the  coupling  of  A  and  S  are  to  be  found  in  crosses  70-1  to  9, 
71-1  to  6,  72-1,  2,  3,  4,  5,  6,  8,  9, 10,  64-1,  and  74-1.  Repulsion  data  is 
to  be  found  in  64-3  and  72-5. 

TABLE  59. 


Ag-C 

ASas 

Ag-A 

Asas 

B-C 

aSas 

B-A 

asas 

Cross- 
overs. 

Link- 
ages. 

Ag-C,  D            B-Sm  (4-toe) 
Ag-Sm  (i  cut)            B-RfA 
Coupling  —          ASas           X          asas  

12 

16 

16 

16 

32 

28 

Repulsion  —         AsaS           X          asas  

1 

3 

3 

1 

35 

29 

A  and  S  are  quite  clearly  independent  of  each  other. 

Crosses  72-5  to  7  give  a  few  data  on  the  relation  of  R  and  S  to  C. 
We  find  in  the  case  of  R  and  C,  4  linkages  to  4  cross-overs  and  in  the 
case  of  S  and  C  no  linkages  and  3  cross-overs,  indicating  probably 
independence  in  both  cases. 

From  cross  72-7  we  find  that  cross-overs  can  occur  between  R  and  E, 
R  and  B,  and  S  and  B.  From  61-1  we  find  that  cross-overs  can  occur 
between  P  and  R,  and  P  and  S. 

Summing  up :  R  is  quite  certainly  independent  of  S  and  A  and  cross- 
overs are  known  between  it  and  all  of  the  other  known  factors  E,  B,  C, 
and  P.  S  is  quite  certainly  independent  of  A  and  cross-overs  are  known 
between  it  and  B,  C,  and  P,  but  not  as  yet  E.  It  is  hoped  that  more 
definite  statements  can  soon  be  made  on  these  points. 


ROUGH   FUR. 
SUMMARY  OF  ROUGH  TABLES. 


115 


Table  60,  in  which  smooths  are  omitted,  shows  the  closeness  of  fit 
of  the  hypothesis  to  the  data  as  regards  the  inheritance  of  variations 
of  the  rough  character. 


TABLE  60. 


Cross. 

88   X  88 

A 

B 

C 

D 

E 

45 

A       4-toe  A        4-  toe  

10 

46 

A       Tri  A        Tri  

27 

? 

49 

A       4-toe  Sm     4-toe  

28 

1 

50 

A        Tri  Sm     4-toe  

19 

58 

B        Lima  B         Lima  

7 

ft 

'59 

A        Lima  Sm     Lima  

21 

5 

260 

B        Lima  Sm     Lima  

5 

9 

63 

A,  B  Lima  Sm     4-toe,  etc  

4 

4 

"65 

A          Mipfi  .......,,.,      Sm      M'sn  ........... 

17 

66 

A        Misc  Sm     Misc  

14 

1 

73 

A        J  cut  Sm     4-toe  

2 

75 

A        J  cut  A        J  cut  

3 

Total  

157 

?,7 

Expectation  ss  

18- 

I 

D 

0 

Cross. 

Ss  Xss 

A 

B 

c 

D 

E 

47 

C        Tri  A       Tri,  4-toe  

10 

1 

5 

1 

451 

Sm     Tri  A        

6 

3 

3 

54 

C,  D  Tri  Sm     4-toe,  etc  

34 

?9 

13 

1 

58 

C        Lima  B        Lima  

1 

1 

559,  60 

Sm     Lima  A,  B  Lima  

4 

1 

3 

61 

C        Lima  ....        .         Sm     Lima  

2 

1 

1 

64 

C        ruf  .  hybrid  Sm     4-toe,  etc  

3 

?! 

865 

Sm     ruf.  hybrid  A        

1 

1 

?, 

770 

C,  D  i  cut  A       G.  p  

8 

3 

8 

? 

91 

771 

Sm     J  cut  A       G.p  

10 

3 

9 

1 

72 

C,  D  i,  }  cut  Sm     G.p  

12 

6 

6 

74 

Sm     i  cut  .      .                 A       J  cut  

1 

Total  

90 

11 

69 

?:7 

3 

Expectation  ss  +  Ss  

10 

0 

1 

TO 

0 

Cross. 

Ss  X  Ss 

A 

B 

C 

D 

E 

62 

C  Tri  C  Tri  

18 

6 

19 

7 

1? 

76 

C  f  cut  C  i  cut  

1 

3 

1 

Total  

18 

6 

?0 

10 

13 

Expectation  ss  +  2  Ss  +  SS  

r 

r 

3 

I 

17 

Emitting  young  of  L24. 
*Omitting  young  of  L6,  L24. 
^Omitting  young  of  A702,  A605. 
4Some  of  mothers  may  be  ss  or  SS. 


•Mothers  L24,  L6. 
•Mothers  A702,  A605. 
'Including  also  one  J  cut. 


116 


INHERITANCE   IN   GUINEA-PIGS. 
TABLE  60 — Continued. 


Cross. 

SB  X  SS 

A 

B 

C 

D 

E 

48 

A  Tri                                  E      Tri    

? 

1 

56 

Sm  4-toe                            E      Tri  

13 

67 

A  4-toe,  tri                         Sm  pure  lea       

5 

68 

A                                           Sm   pure  cut  .          .  . 

8 

6 

Total 

23 

7 

Expectation  Sa  

C 

1 

3 

0 

0 

Cross. 

Ss  XSS 

A 

B 

C 

D 

E 

53 

C  D  Tri                   .         E      Tri 

4 

1 

6 

>      69 

C,  D  Tri  Sm  pure  cut  

1 

1 

9 

Total  

5 

2 

15 

Expectation  Ss  +  SS  

( 

1 

] 

1 

11 

Cross. 

SS  XSS 

A 

B 

C 

D 

E 

55 

E  Tri  E  Tri  

4 

Expectation  SS  

( 

1 

( 

1 

4 

The  interpretation  given  is  no  doubt  open  to  objections.  In  some 
cases  the  ratios  seem  rather  aberrant.  This  is  in  part  due  to  the  small 
numbers,  but  also  to  the  overlapping  of  class  ranges.  In  most  cases 
rough  B  must  be  considered  as  full-rough  genetically  (Rss),  but  in  some 
cases  it  is  probably  partial-rough  (RSs) .  Rough  E  usually  seems  to  be 
RSS,  but  in  some  cases  must  be  heterozygous  (RSs).  It  has  not  been 
demonstrated  that  factor  S  of  the  wild  species  is  identical  with  the 
similar  factor  of  the  tricolor  stock.  If  not  identical,  however,  the 
latter  stock  differs  from  the  wild  by  two  mutations  which  neutralize 
each  other,  while  if  identical  we  can  consider  that  the  original  tricolor 
stock  had  simply  persisted  in  the  primitive  condition,  never  having 
had  the  rough  intensifying  mutation,  s,  of  the  fancier's  roughs. 

MINOR  VARIATIONS. 

Probably  part  of  the  minor  variations  in  roughness  are  due  to  chance 
irregularities  in  development  which  are  not  hereditary.  This  is  indi- 
cated by  the  slight  asymmetry  not  uncommonly  present.  This  asym- 
metry seldom  amounts  to  more  than  the  absence  of  a  member  of  one 
pair  of  rosettes. 

No  Mendelian  analysis  has  yet  been  attempted  for  minor  variations, 
but  certain  hereditary  differences  between  different  stocks  are  quite 


ROUGH   FUR. 


117 


clear.  The  Lima  stock  shows  a  distinctly  lower  level  of  development 
of  roughness  than  is  found  in  the  4-toe  stock  or  even  among  the  full- 
roughs  of  tricolor  stock.  A  large  part  of  the  variation  and  overlapping 
in  the  remaining  experiments  in  which  various  stocks  have  been  mixed 
is  made  intelligible  by  assuming  that  the  residual  heredity  is  unfavor- 
able for  roughness  in  the  wild  species  and  especially  favorable  in  the 
4-toe  stock.  If  we  let  S+  stand  for  favorable  and  S  —  for  unfavorable 
residual  heredity,  the  wild  species  and  presumably  the  primitive 
guinea-pigs  are  rrSSS  — ,  while  the  good  fancier's  roughs,  RRssS-j- 
differ  by  at  least  three  independent  sets  of  factors,  all  favorable  for 
roughness. 

ROUGHNESS  OF  SERIES  II. 

It  has  been  mentioned  that  irregularities  in  hair  direction  have  been 
found  in  certain  stocks  which  can  not  be  classified  by  the  grades  which 
have  been  defined.  The  BW  race  is  a  highly  inbred  race.  No  indi- 
viduals of  the  pure  stock  have  ever  been  observed  to  have  roughness 
on  the  face,  back,  or  toes,  but  many  of  them  show  irregular  partings 
and  crests  along  the  chest  and  belly.  It  will  be  remembered  that  hi 
series  I  ventral  roughness  appears  only  in  high-grade  roughs — grades 
A  or  B.  Thus  the  characteristic  roughness  of  the  BW  stock  is  nearly 
the  least  characteristic  feature  of  series  I. 

The  only  distinction  which  has  been  made  in  these  BW  roughs  is 
between  strong-rough  with  two  or  more  ridges  and  poor-rough  with 
only  one  ridge  or  a  mere  trace  of  roughness.  Table  61  shows  the 
principal  results. 

TABLE  61. 


Smooth. 

Poor 
rough. 

Strong 
rough. 

Smooth  X  smooth  
Poor        X  poor  

11 
14 

6 
1 

6 
1 

Strong    X  strong  ...    . 

5 

5 

16 

It  is  clear  that  this  roughness  is  due  neither  to  a  simple  dominant 
nor  to  a  simple  recessive.  Aside  from  this,  the  results  are  exceedingly 
difficult  to  interpret,  since  poor  X  poor  gives  more  smooth  than  does 
smooth  by  smooth.  Probably  the  results  will  become  more  harmonious 
when  more  data  are  obtained.  It  seems  safe  to  conclude  at  present  that 
this  roughness  is  wholly  independent  of  ordinary  roughness  in  its 
causation. 

Irregularity  in  hair  direction  on  the  back,  not  resembling  anything 
hi  series  I  and  not  correlated  with  roughness  of  the  hind  toes,  has 
been  observed  in  a  few  individuals  of  Arequipa  and  lea  stock.  It  does 
not  seem  to  be  like  the  BW  roughness,  but  resembles  the  latter  in  the 
irregularity  of  its  inheritance. 


118  INHERITANCE   IN   GUINEA-PIGS. 

SUMMARY. 

The  principal  results  which  have  been  reached  may  be  summarized 
as  follows: 

1.  A  classification  of  guinea-pig  fur,  skin,  and  eye  colors  is  given  with 
definitions  of  fur  colors  in  terms  of  Ridgway's  charts  (1912). 

2.  Rodent  color  factors  are  conveniently  classified  as  follows : 

a.  Factors  which  affect  the  distribution  and  intensity  of  color  largely  irrespective 

of  the  kind  of  color. 

b.  Factors  which  govern  the  differentiation  between  yellow  and  dark  colors  in 

colored  areas  of  the  fur. 

c.  Factors  which  determine  the  kind  of  dark  color  in  the  areas  with  dark  pigmenta- 

tion in  fur  and  eyes,  without  influence  on  yellow  areas. 

Definitions  of  all  known  guinea-pig  color  factors  are  given  on  this 
basis  and  a  table  of  the  color  varieties  arising  from  combinations  of 
these  factors  is  given. 

3.  Genetic  and  biochemical  evidence  on  the  physiology  of  pigment 
formation  suggests  the  hypothesis  that  the  three  groups  of  factors 
determine  respectively  the  distribution  and  rate  of  production  by  the 
nucleus  of  the  following  substances : 

o.  A  peroxidase  which,  acting  alone,  oxidizes  chromogen  in  the  cytoplasm  to  a 
yellow  pigment  but  is  so  unstable  that  it  must  be  produced  at  a  relatively 
high  rate  to  give  any  pigment  at  all. 

b.  A  supplementary  substance  which,  united  with  the  first,  makes  it  a  dark-pig- 
ment-producing enzyme  and  of  such  stability  that  color  develops  at  a 
much  lower  level  of  production  of  peroxidase  than  when  the  supplement 
is  absent.  Above  the  level  at  which  both  produce  effects,  the  dark  and 
yellow-producing  enzymes  compete  in  the  oxidation  of  chromogen. 

e.  Additions  to  the  second  substance  which  cause  variations  in  dark  color  but  not 
in  yellow  or  in  the  competition  between  dark  color  and  yellow. 

4.  There  is  a  continuous  series  of  variations  in  intensity  of  pigmen- 
tation hi  the  yellow,  brown,  and  black  series  and  in  eye  color.    The 
ordinary  dilute  guinea-pigs  are  found  to  be  imperfect  albinos  in  the 
sense  that  dilution  is  due  primarily  to  a  member  of  the  series  of  allelo- 
morphs— intensity,  dark-eyed  dilution,  red-eyed  dilution,  and  albinism, 
with  dominance  in  the  order  of  increasing  intensity. 

5.  A  further  step  in  the  analysis  of  the  continuous  series  of  variations 
of  intensity  is  taken  hi  the  demonstration  that  dilution  is  imperfectly 
dominant  over  red-eye  and  albinism  as  regards  the  yellow  series  of 
colors,  and  that  dilution  and  red-eye  are  imperfectly  dominant  over 
albinism,  as  regards  the  black  series.    Smaller  effects  are  due  to  the 
residual  heredity  of  different  stocks  and  to  age. 

6.  Evidence  is  presented  which  confirms  the  hypothesis  of  Detlefsen 
(1914)  that  the  light-bellied  agouti  pattern  of  tame  guinea-pigs,  the 
ticked-bellied  agouti  of  hybrids  between  the  tame  guinea-pig  and  Cavia 
rufescens,  and  non-agouti  (as  seen  in  self  blacks  or  browns)  form  a 
series  of  triple  allelomorphs  in  which  light-belly  is  the  highest  dominant 
and  non-agouti  the  lowest  recessive.    Evidence  is  presented  which 


GENERAL    CONCLUSION.  119 

indicates  that  Cavia  cutleri  possesses  the  same  agouti  factor  as  tame 
agouti  guinea-pigs.  Light  agouti  of  Cavia  cutleri  and  dark  agouti  of 
Cavia  rufescens  are  thus  variations  in  a  character  in  two  wild  species 
which  differ  in  heredity  by  a  clear-cut  Mendelian  factor.1 

7.  There  is  a  continuous  series  of  variations  between  smooth  fur 
and  very  rough  or  resetted  fur  in  guinea-pigs.  The  primary  effects  in 
this  series  are  due  to  two  independent  pairs  of  allelomorphs.  One 
factor,  discovered  by  Castle  (1905),  is  essential  to  any  roughness  of  the 
common  type,  and  is  completely  dominant  over  its  allelomorph  found  in 
wild  cavies  and  smooth  guinea-pigs;  the  other,  an  incomplete  recessive 
to  its  allelomorph  in  the  wild  cavies  and  some  tame  guinea-pigs,  is 
necessary  for  the  higher  grades  of  roughness.  Second-order  effects 
seem  to  be  due  to  the  residual  heredity  of  different  stocks,  and  probably 
to  non-hereditary  irregularities  hi  development.  There  is  a  roughness 
of  a  different  type  from  the  usual  which  is  inherited  independently. 

GENERAL  CONCLUSION. 

Most  of  the  successful  earlier  attempts  at  Mendelian  analysis  of 
heredity  naturally  dealt  with  variations  which  were  obviously  dis- 
continuous. But  in  nature  such  variations  are  much  less  common  than 
apparently  continuous  series  of  variations.  It  was  thus  a  common 
reproach  against  the  Mendelian  analysis  that  it  dealt  only  with  excep- 
tional conditions.  The  work  of  Nilsson-Ehle,  East,  and  others  has 
shown  how  quantitative  variation  may  be  brought  under  a  Mendelian 
explanation.  MacDowell  (1914)  presents  data  on  size  inheritance 
from  this  standpoint  and  discusses  the  literature  up  to  that  time. 
Recently  two  very  interesting  papers  have  been  published  (Dexter,  1914, 
Hoge,  1915)  which  analyze  the  heredity  of  certain  very  variable  char- 
acters in  Drosophila  by  means  of  linkage  relations. 

Several  of  the  studies  in  this  paper  deal  with  inheritance  in  continu- 
ous series  of  variations.  The  only  general  statement  which  can  be 
made  about  the  results  is  that  there  is  no  general  rule  for  such  cases. 
Intermediates  between  varieties  which  mendelize  regularly  have  been 
found  to  follow  very  definite  modes  of  inheritance,  which,  however,  are 
very  different  in  different  cases  and  could  not  possibly  be  predicted 
a  priori.  On  the  other  hand,  each  mode  of  inheritance  is  exactly 
paralleled  by  cases  among  the  most  diverse  groups  of  animals  and  plants. 
It  may  be  interesting  to  summarize  the  modes  of  inheritance  of  inter- 
mediates which  have  been  found. 

An  intermediate  condition  is  sometimes  found  to  be  due  to  an  inter- 
mediate variation  of  the  essential  hereditary  factor  involved,  i.  e.,  to 
an  allelomorph.  Thus  yellows  are  intermediate  between  red  and  albino 

1  It  should  be  pointed  out,  however,  that  the  original  stock  of  Cavia  rufescens  used  in  these  experi- 
ments included  individuals  of  the  light-agouti  character  as  well  as  those  classed  as  dark  agouti. 
It  seems  quite  likely  that  dark  agouti  arose  as  a  recessive  mutation  in  C.  rufescens. — W.  E.  C. 


120  INHERITANCE   IN   GUINEA-PIGS. 

guinea-pigs  in  appearance,  and  we  find  an  allelomorph  intermediate  in 
dominance  between  the  intensity  and  albino  factor  to  be  responsible 
for  their  condition.  Sepias  are  similarly  intermediate  between  blacks 
and  albinos  and  are  due  to  the  same  allelomorph  of  intensity  and  albin- 
ism. The  series,  light  agouti  of  Cavia  cutleri,  dark  agouti  of  C.  rufes- 
cens,  and  black,  furnishes  another  example  due  to  triple  allelomorphs. 

In  other  cases,  the  intermediate  type  is  an  unfixable  one,  due  to 
imperfect  dominance.  Thus  cream  is  the  heterozygote  between  yellow 
and  albino.  A  "razor  back"  rough  (rough  C  or  D)  is  the  heterozygote 
between  a  type  smooth  except  for  the  hind  toes  (rough  E)  and  a  full- 
rough  (rough  A). 

A  series  of  deviations  from  the  original  type  may  depend  on  the 
presence  of  a  certain  factor  necessary  for  any  deviation  whose  effect  is 
modified  to  different  extents  by  independently  inherited  factors. 
Rough  A  contains  the  same  rough  factor  (R)  as  does  rough  E,  but  differs 
in  possessing  an  independent  factor  variation  (s)  favorable  for  rough- 
ness. Most  of  the  variation  which  we  have  ascribed  to  residual 
heredity  probably  comes  under  this  head. 

Deviations  from  type,  which  apparently  form  a  natural  series,  may 
be  due  to  wholly  independent  factors  whose  effects  are  merely  super- 
ficially similar.  A  pink-eyed  pale  sepia  superficially  seems  as  good  an 
intermediate  between  an  intense  black  and  an  albino  as  does  a  black- 
eyed  sepia,  yet  the  former  is  due  to  a  variation  which  is  wholly  inde- 
pendent of  albinism;  the  latter  is  due  to  an  allelomorph  of  albinism. 
White-spotted  animals  are  sometimes  called  partial  albinos  and  con- 
sidered as  natural  intermediates  between  the  self-colored  type  and 
albinos,  but  genetically  they  are  wholly  distinct.  Black,  agouti,  and 
self  yellow  form  a  series  which  is  due  to  three  allelomorphs  in  mice,  but 
in  guinea-pigs  two  wholly  independent  sets  of  factors  are  involved. 

Finally,  we  must  recognize  series  of  variations  in  which  no  Mendelian 
factors  have  yet  been  isolated.  The  series  of  white-spotted  and  yellow- 
spotted  types  and  the  series  of  polydactylous  types  are  examples  hi 
guinea-pigs.  Further,  in  all  series  of  variations,  to  whatever  extent 
analysis  has  been  carried,  there  always  remains  some  unanalyzed  varia- 
tion. In  many  cases  such  variations  are  known  to  be  hereditary  and 
can  be  assigned  to  the  residual  heredity  of  particular  stocks.  Such 
unanalyzed  variations,  however,  are  probably  in  general  complicated 
by  variation  which  is  not  hereditary,  due  apparently  to  irregularities 
hi  development.  If  we  can  measure  the  importance  of  such  non- 
hereditary  variation  by  the  extent  of  irregular  asymmetry  met  with,  it 
is  very  important  in  white  and  yellow  spotting,  in  the  variations  in  the 
development  of  extra  toes  on  the  hind  feet,  and  is  noticeable  in  varia- 
tions in  roughness. 

In  the  continuous  series  of  variations  several  of  these,  phenomena 
have  generally  been  found  together.  In  the  series  from  smooth  to  full- 


TABLES.  121 

rough  we  find  a  primary  unit  difference,  a  modifying  factor,  imperfect 
dominance  in  the  effects  of  the  latter,  effects  of  residual  heredity,  and 
probably  some  non-heritable  variation.  In  the  series  from  red  through 
yellow  and  cream  to  white  we  find  multiple  allelomorphs,  imperfect 
dominance,  and  small  effects  due  to  residual  heredity.  In  the  series 
black  through  sepia  to  white,  we  find  independent  factors,  multiple 
allelomorphs  which  show  imperfect  dominance,  and  rather  prominent 
effects  due  to  residual  heredity  and  to  age.  This  last  series  is  interesting 
as  at  least  a  close  parallel  in  appearance  to  the  series  of  variations  in 
human  hair — black,  brown,  tow-color,  to  white.  Thus  hi  each  case  a 
complex  of  the  most  varied  causes  underlies  an  apparently  simple 
continuous  series  of  variations. 

EXPERIMENTAL  DATA. 
EXPLANATION  OF  TABLES  62  TO  137. 

Crosses  1  to  15  include  all  matings  recorded  by  the  writer  which 
involve  the  inheritance  of  agouti  and  in  which  at  least  one  of  the  parents 
had  Cavia  rufescens  ancestry.  A  large  part  of  the  remaining  crosses  are 
non-agouti  by  non-agouti,  producing  only  non-agouti  young.  All  the 
young  in  which  the  agouti  factor  should  produce  a  recognizable  effect, 
if  present,  are  classified  under  the  heads  Lb,  Tb,  and  Non,  which  mean 
light-bellied  agouti,  ticked-bellied  agouti,  and  non-agouti,  respectively. 
Most  of  these  are  the  typical  (black-red)  light-bellied  or  ticked-bellied 
agouti  or  black.  Those  which  are  not  typical,  e.  g.,  brown-red  agouti 
light-belly,  red-eyed  sepia,  etc.,  are  described  further  under  the  column 
"  Remarks."  Those  young  in  which  the  agouti  factor  can  produce  no 
visible  effect,  even  though  present  (albinos,  reds,  yellows,  and  creams), 
are  described  under  the  column  " Unclassified."  Thus  the  exact  color 
of  every  one  of  the  young  from  each  mating  can  be  found  from  the 
tables,  with  the  exception  that  white  and  red  spotting  are  not  noted. 
The  matings  in  each  cross  are  numbered  in  the  first  column.  The 
number,  description,  and  descent  of  the  mother  and  father  are  given  in 
the  second  and  third  columns,  respectively.  As  in  the  case  of  the 
young,  black-red  agouti  light-belly  or  ticked-belly  or  black,  depending 
on  the  heading  of  the  column,  are  understood  where  no  description  is 
given.  The  descent  is  indicated  in  most  cases  by  a  reference  to  the 
mating  from  which  the  animal  was  derived.  Thus  36-4  means  mating 
4  of  cross  36.  In  other  cases  the  stock  is  indicated  as  BB  or  BW.  The 
symbol  ArF2  means  F2  from  crosses  of  Arequipa  c?  1002  with  guinea- 
pigs.  In  some  cases  merely  the  amount  of  Cavia  rufescens  blood  is 
given.  Thus  M49,  in  the  first  cross  given,  was  an  ordinary  ticked- 
bellied  agouti  from  mating  9  of  cross  la.  Referring  to  this  mating, 
we  see  that  his  parents  were  female  84,  a  black  of  BB  stock,  and  male 
A1121,  a  ticked-bellied  agouti  with  ^  Cavia  rufescens  blood. 


122 


INHERITANCE  IN   GUINEA-PIGS. 


Crosses  16  to  44  include  all  matings  recorded  by  the  writer  in  which 
there  was  dilution  or  red-eye  in  either  parents  or  offspring,  except  for  a 
few  cases  among  the  Cavia  cutleri  hybrids  and  cases  of  intense  by  dilute 
with  only  intense  young.  Some  other  crosses  are  included  for  special 
reasons  bearing  on  the  inheritance  in  the  albino  series.  There  is  some 
repetition  from  matings  outside  of  16  to  44,  but  most  of  those  outside 
are  intense  by  intense,  with  only  intense  and,  in  some  cases,  albino 
young.  As  in  the  agouti  crosses,  all  matings  are  numbered  in  column  1. 
The  number,  description,  and  descent  of  the  mother  and  father  are 
given  in  columns  2  and  3,  respectively.  All  the  offspring  are  classified 
under  the  heads  Int,  Dil,  RE,  or  W,  which  stand  for  intense,  dilute, 
red-eye,  and  white  (albino),  respectively.  A  further  description  of  all 
except  the  albinos  is  given  under  the  column  "  Remarks."  The 
attempt  has  been  made  to  give  the  grade  of  dilution  at  birth  for  every 
dilute  or  red-eyed  animal  where  known. 

Crosses  45  to  57  give  the  data  on  the  inheritance  of  rough  fur  in  the 
4-toe  and  tricolor  stocks.  As  before,  the  matings  are  numbered.  The 
young  are  classified  under  the  heads  A,  B,  C,  D,  E,  and  Sm,  which  refer 
to  the  grades  of  roughness  defined  in  the  paper  and  to  smooth. 

The  parents  and  offspring  were  black  (usually  with  red  and  white 
blotches)  except  for  a  few  cases  which  are  all  noted.  Such  a  symbol  as 
red-B  means  a  red  of  grade  rough  B. 

Crosses  58  to  62  give  the  results  in  the  pure  Lima  stock  and  63  the 
results  in  the  cross  of  Lima  with  other  stocks.  Where  no  color  is  given 
black  is  always  to  be  understood. 

Crosses  64  to  66  give  the  matings  involving  rough  fur  among  Cavia 
rufescens  hybrids  which  were  recorded  by  the  writer. 

Cross  67  gives  crosses  of  pure  lea  with  rough  A  stock. 

Crosses  68  to  78  give  all  the  data  in  matings  involving  Cavia  cutleri 
ancestry  made  by  the  writer. 

The  following  symbols  are  used : 

AgLborAg  =  Black-red  agouti,  light-belly. 


AgTb  =  Black-red  agouti,ticked-belly. 

B  =  Black. 

BrAgLb       =  Brown-red  agouti,  light-belly. 

BrAgTb       =  Brown-red     agouti,     ticked 
belly. 

Br  =  Brown. 

R  =  Red  (black-eye). 

R(Br)  =  Red  (brown-eye). 

SYAgLb      =  Sepia-yellow     agouti,     light- 
bdly. 
=  Sepia-yellow  agouti,   ticked- 

belly. 
=  Sepia. 


SYAgTb 
Sep,  S 


SAg(R) 
Sep(R) 
W 

Red(p) 
Sep  (p) 

In  such  expressions  as  S3Y3Ag  the  numerals  stand  for  the  grades  defined  in  the  text. 
In  crosses  1-15,  Lb  and  Tb  are  used  at  the  heads  of  the  columns  to  include  any  light-bellied 
or  ticked-bellied  agouti.     Non  means  non-agouti. 

A,  B,  C,  D,  E,  and  Sm  are  used  for  grades  of  roughness  and  for  smooth. 


BrYAgLb    =  Brown-yellow    agouti,  light- 
belly. 
BrYAgTb    =  Brown-yellow  agouti,  ticked- 

belly. 

LBr  =  Light  brown. 

Y  =  Yellow  (black-eye). 

Y(Br)  =  Yellow  (brown-eye). 

Cr  =  Cream,  used  in  compounds 

likeY. 

=  Sepia-white  agouti  (red-eye). 
=  Sepia  (red-eye). 
=  White  or  albino. 
=  Red  (pink-eye). 
=  Sepia  (pink-eye). 


TABLES. 


123 


TABLE  62. 
Cross  1. — Matings  of  non-agouti  (aa)  with  ticked-bellied  agouti  (A 'a). 

Each  of  the  latter  known  to  be  heterozygous  because  of  a  non-agouti  parent. 
Expectation:  A'a  X  aa  =  A'a  +  aa  (1  AgTb :  1  Non-Ag). 


la.  Mother  non-agouti,  without  rufescens  ancestry. 

No. 

9  Non-Ag. 

rfAgTb. 

Lb. 

Tb 

*Jon 

Remarks. 

Unclas- 
sified. 

1 
2 
3 

4 
6 
6 
7 
8 
9 
10 
11 
12 
13 
14 

15 
16 
17 
18 

399            BW... 
499           4-toe.  . 

M49                    la 
Do 

-q 

9 
5 
3 
2 
4 
1 
6 
9 
1 

9 

8 
9 
2 
3 
2 
4 
4 
2 
5 

6  W 
1  W 
5  W 
1  W 
2  W 

399           BW.  .  . 
399           4-toe. 

B5                       ld-16. 
Do             ...---- 

299           BW.  .  . 
65                 BB  .  .  . 
299           BW.  .  . 
399           BW.  .  . 
84                 BB  .  .  . 
C22              Misc.. 
C35              Misc.. 
399            4-toe.  . 
3W              BW... 
3  W              Misc  .  . 

D44Sep      16o-3. 
AA244  Sep  2-12 

B27                     Id 
B30                     la 
B69                     la 
B191                    la 

A1121                        & 

A1474                  ft 
Do 

-14. 
-1 

-1 

2  W 
4  W 

-5 

? 

B171                    la 
B117SCrAgTb  Id 
Do 

-4 

8 
3 
2 

1 

6 
2 
3 

1  W 
5  W 
1  W 

2  W 

-11. 

3  SCrAgTb, 
SCrAgTb.Bi 
3  Sep. 
SCrAgTb 

2  Sep  

•CrAgTb, 

Do 

Do 

1 

SCrAgTb 

BW  43  W    BW.  .  . 

Sep  (R)        S.Am  . 

Total 

D113BCrAgTb  3a-7  . 
AA433a                3b-A  . 

1 

4 

1 
2 

SCrAgTb,  S 
3  AgTb,  SAg 
Sep(R). 

»p  

Tb(R),  2 

1  W 

62 

62 

Ib.  Mother  non-agouti,  with  rufescens  ancestry. 

No. 

9  Non-Ag. 

cfAgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclassified. 

1 
2 
3 

4 

5 
6 

7 
8 

9 

10 
11 

A443          £  

A469     |  

1 
1 

LI 

tr  

A1390        A  
A1227W  ^  
/A1413        &  
\A1291W  A  
A1309  W  tf  
A1407        5!,  
A1413        ^  
M115W    ^  
fM114         16-7... 

A1050  g'j  

A781     Jz.. 

3 

SC 

rAgTb  

^A1449  T&  .  . 

1 

1 
3 
3 
1 

2 

1 
2 
1 

W 

R,  R(Br),  Cr(Br) 

A1513  &  

Br 
Br 

AgTb  

A1449  s>j  

Do  
M189    lc-3  

1  Do.. 

4 
1 

4 
1 

SC 
Br 

rAgTb,  Sep  .  . 

\M90  Br     
M90Br     jfe  

/ 

Do  

CrAgTb,  Sep 

Cr 
W 

A1330        its---- 
Total 

A1331  fiff.. 

17 

13 

124 


INHERITANCE   IN   GUINEA-PIGS. 
TABLE  62 — Continued. 


Ic.  Male  genetically,  but  not  visibly  ticked-bellied  agouti. 

No. 

9  Non-Ag. 

tfAgTb. 

Lb 

Tb 

Noi 

i                Remarks. 

Unclas- 
sified. 

1 

2 
3 
4 

5 
6 
7 
8 
9 

131  W            G.p.. 
13a                 G.p.. 
20                   G.p.. 
58  Sep             Dil  .  . 
17,  30Cr(B)  Dil    . 

A412  R(] 
Do 

Br)  Ar. 

2 
3 

Se 

p  

Do  

3 
3 

1 
1 

SC 
3£ 
Se 
SC 
SC 

*Ag1 
5CrA 
p.  .  . 

rb  

B42  W           la-3  .  . 
Do  

?Tb  

2  W 
W 

55  Cr(Br)       Dil    . 

Do  . 

1 

*AgT 
*Ag1 

"b  

M292              &... 
M326              jV 

D18W 
Do 

lc-5  .  . 

2 
1 
1 

3 
1 
1 

:b,  2  Sep.  .  . 

4  W 

M353              fa 

Do  

Se 

p  

Total  

11 

12 

Id. 

Male  non-agouti,  without  rufescens  ancestry. 

No. 

9  AgTb. 

cf  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 

^606  AgLb         J  . 

166    4-to 
2966  BB 
3013  BB 
Do 

e  

? 

IA450  AgLb         i  . 

M 

1 

A340                     & 
A341                      & 
A357                     ^ 
A1146                   & 
A1058                   sS 
A1171                   & 
A1058,  A1171      sfr 
Do  

4 
6 

1 
7 

1 

3 
5 
2 
6 
1 
2 

...     Do      

.    .     Do 

Do 

Do 

2996  BB 
1357  BW 
.  .  .    .Do  . 

3 
5 
2 
1 

2 
5 
1 

2  W 

A1117                  ^ 
Do 

SCrAgTb.... 

2996  BB 
3013  BB 
1357  BW 
Do 

Do 

2 
2 
3 

1 
1 
9 
1 

4 
1 
1 
1 
2 
11 

A1450                   s1, 
A1117,  A1450      & 
A1582                   ^ 
A1583                   ^j 
A1677                  & 
A1678                   SV 
B8                        Id- 
B23                        Id- 
B26                        Id- 
M113                    Ib- 
M442  BrCrAgTb  11 

Total  

W 

2996  BB 
Do 

Do 

.    .     Do  .... 

-7 

.    .     Do 

3 
5 
2 
2 

2 
7 
1 
1 
2 

-12 

Do 

-14 

Do 

-7 

C20    Mis 
86  WBW 

(» 

j-10  

2  Sep 

ll 

61 

63 

TABLES. 


125 


TABLE  62 — Continued. 


le.  Male  non-agouti  (genetically)  with  rufescens  ancestry. 

No. 

9AgTb. 

c?  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 

A1146  fa  

A504  W    fa  

2 

2  Sep 

B132     ld-3  

M293  Y   42-14  

2 

SCrAgTb 

B95       ld-4  

Do    

1 

B24       ld-4  

Do  

1 

B52       la-3  

M201  W  42-13    .... 

2 

B33       ld-18  

Do  

2 

W 
W 

W 

B110     lo-l  

Do  

Bill     lo-l  

.Do  ... 

1 
1 

2 

B128     lo-l  

Do  

B23       ld-12  

Do  

1 

Total 

10 

5 

,  but  agouti  known  to  be  derived  from  C.  rufescens. 

SUMMAKY    OF    CROSS    1. 


No. 

M 

A'a 

Lb 

Tb 

Non 

la 

9  9  Non-Ag  (g.p.)  .... 

cf  d"AgTb  

62 

62 

16 

9  9  Non-Ag  (hybrid)  .  . 

cfcfAgTb  

17 

13 

le 

9  9  Non-Ag  

d"  cTA'a  (R  or  W)  .  .  . 

11 

12 

Id 

d"  cT  Non-Ag  (g.p.)  .... 

9  9  AgTb  

1 

61 

63 

le 

d"  c?aa(Y  or  W)  hybrid 

9  9  AgTb  

10 

5 

Total  

~1~ 

161 

155 

TABLE  63. 
Cross  2. — Matings  of  ticked-bellied  agouti  (A'a)  with  ticked-bellied  agouti  (A'a),  in  which 

both  are  known  to  be  heterozygous  because  of  the  parentage  in  each  case. 
Expectation:  A'a  X  A'a  =  A'A'  +  2A'a  +  aa  (3AgTb :  1  Non-Ag). 


No. 

9  AgTb. 

cT  AgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

B15                        ld-6.. 

B118                      ld-6.. 

1 

2 

2 

B58                        ld-15. 

Do  

9 

2 

3  BrAgTb, 

3 

B59                        ld-15. 

Do  

6 

4 

SYAgTb.Sep 
2  BrAgTb  

4 

B68                        la-1  .  . 

Do  

5 

2 

SCrAgTb  

5 

A529  BrAgTb      fa  

AA15                     fa.. 

6 

1 

BrAgTb,  SCr 

6 

A913                     fa  

Do  

5 

AgTb,  BrCr 
AgTb 
BrAgTb  

7 

A1273  SCrAgTb  fa  

AA16                     fa.. 

4 

2 

3  SCrAgTb  .  .  . 

3W 

8 

Do  

A1121                    fa  

1 

9 
10 

A780                     fa---- 
A1306                    Tiit.. 

A781                       fa---- 
A  1307 

6 
1 

BrYAgTb  

3R.Y 
2W 

11 

A1561                    fa  

A1050                    fa  

3 

4W 

12 

A1566                   fa  

.    .  Do              

5 

1 

BrAgTb,  SCr 

12a 

A1566 

AA15                     fa.. 

2 

1 

AgTb,  Sep 
SCrAgTb  

13 

A702                     fa  

AA16                     fa 

2 

2 

Br     . 

14 

A1450                   fa  . 

AA433a                 36-4 

1 

15 

A1058                   fa  

Do  

W 

16 

A1523                     fa  

A1449                    fa  .  .  . 

2 

1 

BrAgTb  

W 

17 

18 

AA176                   41-4.. 
AA175                   41-4.. 

AA177  SCrAgTb  41-i.. 
Do  

5 

1 

SCrAgTb  

W 
W 

19 

M78                       9-5 

A1161                    fa 

2 

20 

MHO                     16-6.. 

A1170                    fa  

1 

21 

D26  SCrAgTb      lc-4.  . 

D33  SCrAgTb       lc-6.. 

W 

Total  

66 

19 

126 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  64. 

Cross  3. — Matings  of  ticked-bellied  agouti  from  cross  2  or  12  (A'A',  2A'a)  with  non-agouti 
(aa)  made  in  order  to  test  for  the  presence  of  homozygotes. 

Expectation:  A'A'  X  aa  =  A'a  (all  AgTb) 

or  A'a  X  aa  =  A'a  +  aa  (1  AgTb :  1  Non-Ag). 


3a.  Heterozygous  females. 

No. 

9  AgTb. 

cf  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
2 
3 
'4 
5 
*6 
»7 
»8 

M19  2-16.. 
M203  2-19  .  . 
AA211  2-6... 
AA240  12-8.. 
AA257  12-2.. 
AA285  SCrAgTb  12-7.  . 
AA242SYAgTb  12-8.. 
AA240,  AA242  ,  |  12-8  .  . 

7  females 

393              4-toe.... 

2 

1 
1 

M116Sep   42-11.  .  . 

C20             Misc.  .  .  . 

2 

A1040          &  

2 
2 

1 
1 
2 

1 

2 
1 
2 
1 

A1040.356  &,  4-toe. 
393               4-toe  . 

I5Sep(R)    21-1 

BCrAgTb,  2  Sep  . 

A1040          & 

10 

11 

36.  Possible  homozygous  females. 

No. 

9  AgTb. 

cf  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
2 
3 
4 
5 

AA209  2-11.. 
AA212  BrAgTb  2-6... 
AA213  2-12.. 
AA217  2-7 

C21  Misc. 

4 

C20  Misc. 

2 

C21   Misc 

8 

Do 

8 

AA298                    2-13  .  . 
5  females 

356    4-toe  

3 



25 

*Not  certain  that  both  parents  were  heterozygous  (A'a) . 


TABLES. 


127 


TABLE  64. — Continued. 


3c.  Heterozygous  males. 

No. 

9  Non-Ag. 

d"AgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

2 

3 
4 
5 
6 

7 

8 
9 
10 
11 
12 
13 

14 

15 

16 
17 
18 
19 
20 
21 

22 
23 
24 
25 
26 

M79  W          g1*  

M77BrAgTb         2-16. 

1 

2 

1 
2 
1 

BrAgTb.Br... 
BrAgTb,  Br..  . 

3  W 

/M72                lc-2  .  .  . 
\M86                9-1   ... 
M42LBr       42-12.. 
M44  Cr         42-12.. 

\  Do.. 

/ 
AA197                    2-10... 

Do  

3 

SCrAgTb  

M99                42-13?  . 
M101              42-13? 

Do  

1 

Do  

2 
5 
1 

1 
3 

/A1407             A 

JAA199  SCrAgTb   2-12 

\A1413             &  
S6                    ,K.... 
S15                 ,1* 

AA223  BrYAgTb  2-9  .  . 

.    ...  Do 

2 
2 

Br  

A1659             ,£ff  

Do  

2 
2 

B9                 Misc... 

Do  

BrAgTb  

S2                   Misc.  .  . 
A1665             Misc.  .  . 

AA226                     2-13  .  .  . 

1 

Do  

1 
3 

2 
1 
13 

R 

S22,  A1674  ('t8  
liis-  •  •  • 
B7                   ld-7... 
B21                  Id-Q. 

i  Do.. 

/ 
AA235                      12-1  .  .  . 

M 

Do  

2 

B28                 ld-14   . 

Do  

1 

W 
W 
W 

M168             ^j... 

Do  

M169              &... 

Do  

1 

M177              lc-2 

Do  

2 
2 

3 

4 

3 
6 

4 

i 

1 
2 

BrAgTb,  LBr  . 
SCrAgTb,  Sep, 
LBr. 
Br 

499              Misc.  .  . 

B28                 ld-14  .  . 
M183             ^ 

2AA241SYAgTb     12-8.    . 

2AA284                      12-7 

2AA299                     12-8... 
Do 

SCrAgTb 

M261  Sep      7-7 

Sep 

AA58             Vs 

Do 

2 
2 

M261/AA58 

Do 

9  males 

1 

40 

38 

3d.  Homozygous  male. 

No. 

9  Non-Ag.                           d"  AgTb. 

Lb 

Tb 

^on 

Remarks. 

Unclas- 
sified. 

1 
2 
3 

S6           tfa  A, 
S15          •** 

\253  SCrAgTb  2-7  

6 

2  BrAgTb  

Dn 

4 

A1659     8^                     T~)o 

2 

2  SCrAgTb  .  .  . 

1    tlUl  l(  ' 

1?! 

*A  litter  with  an  unexpected  AgLb.     Paternity  not  wholly  certain. 
2Not  certain  that  one  of  parents  was  heterozygous  (A'a). 

SUMMARY  OF  CROSS  3. 


AgTb,  from  cross  A'a  X  A'a, 
tested  by  cross  with  Non-Ag. 

Lb. 

Tb. 

Non 

3a 

79  9  A'a  

10 

11 

3b 

59  9  A'A'(?)  

25 

3c 

go'd*  A'a  

1 

40 

38 

3d 

Icf  A'A'  

12 

128 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  65. 

Cro««  4- — Ticked-bellied  agoutis,  known  to  be  homozygous  because  of  test  (cross  3),  or 
parentage  (cross  4),  crossed  together. 

Expectation:  A'A'  X  A'A'  =  A'A'  (all  AgTb). 


No. 

9  AgTb. 

of  AgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

AA213                  2-12    . 

AA253  SCrAgTb  2-7 

9 

2  SYAgTb, 

? 

AA217                  2-7... 

Do 

11 

SCrAgTb, 
BrAgTb, 
BrYAgTb, 
BrCrAgTb 
3  SYAgTb, 

8 

AA613                 4-1  . 

Do 

3 

SCrAgTb 
3  SCrAgTb  .  .  . 

4 

AA671                 4-1  ... 

Do  

W 

6 

AA577                 4-2... 

AA573  BrAgTb  4-1  .... 

1 

BrAgTb  

6 

AA606  SYAgTb  4-2.  .. 

Do  

2 

SCrAgTb  

Total  

26 

TABLE  66. 

Cross  6. — Homozygous  ticked-bellied  agouti  (A'A')  crossed  with  heterozygous  ticked-bellied 
agouti  (A'a)  or  with  non-agouti  (aa). 

Expectation:  All  AgTb  (A'A'  or  A'a). 


No. 

9  AgTb  or  Non-Ag. 

cfAgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
9, 

M181  BrCrAgTb  15-15.  . 
Do  

AA253  SCrAgTb  2-7... 
AA573  BrAgTb    4-1 

1 
5 

SYAgTb  
3  BrAgTb, 

W 

2  W 

8 

M442  BrCrAgTb  lb-10  .  . 

AA573  BrAgTb    4-1  ... 

1 

2  BrCrAgTb 
BrCrAgTb... 

4 

M296SAgTb         14-4... 

Ml  16  Sep              42-11. 

3 

3  SYAgTb  .  .  . 

5 

D194Sep(R)         26-2... 

AA670  SCrAgTb  4-1  ... 

3 

2  SCrAgTb, 
SAgTb(R) 

2  W 

Total  

13 

TABLES. 


129 


TABLE  67. 

Cross  6. — Matings  of  non-agouti  hybrid  (aa)  with  homozygous  light-bellied  agouti  (AA). 
Expectation:  AA  X  aa  =  Aa  (all  AgLb). 


6a.  Female  non-agouti. 

No. 

9  Non-Ag. 

cTAgLb. 

Lb 

Tb 

Non 

Remarks. 

Unclassified. 

1 
2 
3 

A605  J  

2597  G.p  

?, 

A642  }  

Do  

?, 

A842  J  

Do  

5 

Total 

9 

66.  Male  non-agouti  hybrid. 

No. 

YAgLb. 

cT  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclassified. 

1 

2 
3 
4 
5 

16a                 G.p  .  . 
3520  Cr(Br)  G.p  .  . 
3o                   G.p  .  . 
lla                 G.p.. 
3392               G  p  .  . 

Total 

A674  Sep  J  .  .  . 

6 

Do  
1040         A.. 

3 
7 

2SCrAg,BrCrAg. 

Y(Br),2Cr(Br),W 

A504W   &.. 

3 

A1539      ^.. 

1 
?0 



SCrAgLb  

SUMMARY  OF  CROSS  6. 


No. 

aa  (hybrid). 

AA  (g.p.). 

Lb 

Tb 

Non 

6a 

9  9  Non-Ag.  .  . 

d"  c?  Ag  Lb  

9 

66 

cT  cf  Non-Ag 

9  9  Ag  Lb. 

20 

Total  

29 

130 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  68. 

Cross  7. — Matings  of  non-agouti  (aa)  with  light-bellied  agouti  (Aa)  of  rufescens  ancestry, 
known  to  transmit  non-agouti,  because  of  a  non-agouti  parent. 

Expectation:  Aa  X  aa  =  Aa  +  aa  (1  AgLb :  Non-Ag). 


la.  Female  AgLb. 

No. 

9  AgLb. 

cf  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
2 
3 
4 
5 
6 
7 
8 

9 

10 
11 

12 

A601                    -fa.  . 

103             4-toe... 

1 

1 

W 

A614                    fg  .  . 

224             4-toe... 

2 

A953                     d*   . 

A718          fc  

?, 

3 

A1310                   &. 

166             4-toe  .  .  . 

2 

A1311                   a1*. 

Do  

1 

1 

A1324                  g*z 

A719  W     3>j  

3  W 

M102                   66-1 
Do  

A462W     3^  

2 

2 

2 

Sep. 

M2             A  
J20W          BW.... 
BW  36  W  BW 

3 
3 

SCrAgLb  

/M357SCrAgLb  106- 
\D95  SCrAgLb     106- 
D61  SCrAgLb'    13-5 
D63  SCrAgLb5    13-5 

/D69  SCrAgLb     18-5 
\M425  SCrAgLb  13-7 

Total  . 

7  
*  

3  SCrAg,  2  Sep  . 

7  W 
W 

.....Do  

J....DO  

2 
2 

2 
1 

2SAg(R),Sep, 
Sep(R) 

2  SCrAg,  Sep,  .  . 

W 

14 

18 

76.  Male  AgLb. 

No. 

1  9  Non-Ag. 

cMgLb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

2 
3 
4 

67                   G.p  .  . 
D43  Sep            16a-3  . 
M236Sep(R)  ArF2.  . 
D45  Sep           16a-3  . 

Total  

M123                       13-2.. 
D94  SCrAgLb        106-8  . 
M331  BrCrAgLb  42-10  . 
D94  SCrAgLb       106-8. 

2 
1 

1 
1 

SCrAg,  Sep  .  .  . 

W 
W 

1 

1 

SCrAg,  Ag.... 

4 

3 

SUMMARY  OF  CROSS  7. 


No. 

Aa  (hybrid). 

aa 

Lb 

Tb 

Non 

7a 

9  9  AgLb.... 

cfcf  Non-Ag.  . 

14 

18 

76 

<?(?  AgLb.... 

9  9  Non-Ag  .  . 

4 

3 

Total     . 

18 

21 

TABLES. 
TABLE  69. 


131 


Cross  8. — Matings  of  ticked-bellied  agouti  (A'a)  with  homozygous  light-bellied  agouti  (AA). 
Expectation:  AA  X  A'a  =  AA'  +  Aa  (all  AgLb). 


8a.  Female  AgLb 

No. 

9  AgLb. 

cfAgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

03        G.p  

B5         ld-16  

5 

2 

3392     G.p...            .    .    .    . 

.    ...  Do    

4 

SCrAg  

3 

02,03  G.p  

A1155  ^  

4 

4 

So        G.p  

A1474  ^  

8 

5 

20a      G.p... 

.    .     Do 

4 

SCrAg  

Total  

25 

86.  Male  AgLb. 

No. 

9AgTb. 

c?AgLb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

B33                     ld-18  

2597             G.p  ...    . 

3 

2 

B36                     ld-18  

Do  

6 

3 

B37                     ld-20  

Do  

2 

4 

B52                     la-3  

Do  

3 

5 

/B40W                la-3  

j        Do 

6 

6 

\B37,  B33            above  
A702                   ft  

Do  

2 

7 

A913                   ft  

Do  

2 

g 

1AA606  SYAgTb  4-2        .    . 

724  SAg(R)  (lea)  

2 

2  SYAgLb  .  . 

Total  

?5 

Total  cross  8  

50 

'AA606  was  A'A' 


TABLE  70. 

Cross  9. — Matings  of  light-bellied  agouti  (Aa)  with  ticked-bellied  agouti  (A'a),  both  known 
to  be  heterozygous  with  non-agouti. 

Expectation:  Aa  X  A'a  =  AA'  +  Aa  +  A'a  +  aa  (2  AgLb  :  1  AgTb :  1  Non-Ag). 


No. 

?AgLb. 

cTAgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

3015                 G.p  

A1474  ^  

6 

?, 

5 

3R 

2 

M46  BrCrAg  13-3  

A1170  ft  

2 

BrAgLb  

W 

3 

M57                  13-1  

Do  

1 

1 

4 

A1310               £t  

A1449  ft  

1 

1 

Cr 

5 

Do                 .... 

A1513  ^  

1 

6 

A1311               ft 

A1449  ft     • 

1 

7 

Do 

A1513  ft. 

5 

1 

2 

8 

A1026               ft 

A  1050  ft 

2 

1 

Total  

16 

fi 

10 

132 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  71. 

Cross  10. — Matings  of  light-bellied  agouti  from  such  crosses  as  8  and  9  (AA',  Aa)  with  non- 
agouti,  made  in  order  to  test  whether  light-bellied  agouti  can  transmit  both  ticked- 
bellied  agouti  and  non-agouti. 

Expectation:  AA'  X  aa  =  Aa  +  A'a  (1  AgLb :  1  AgTb). 
or  Aa    X  aa  =  Aa  +  aa    (1  AgLb  :  1  Non-Ag). 


10a.  Females  Aa. 

No. 

9  AgLb. 

c?  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
2 
3 
4 
5 
6 
7 
8 

B120         86-2  

C20              G.p  

<> 

3 

B140         8o-2  

M328B-Y  42-17.... 

3 

1 

Do             

20  W            BW  .... 

3 

2 

M195        9-7     .. 

MllGSep    42-11... 

2 
2 

2  Br  

M217         8a-3  . 

356                4-toe    . 

1 

M282         15-12     .  . 

M116Sep    42-11.... 

AA83            J?  .  .  . 

2 

2 
2 

Sep 

A1562  W  ^i  

A1691        86-7 

Do 

6 

6 

7  females  

17 

20 

106.  Females  AA'. 

No. 

9  AgLb. 

d"  Non-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
2 
3 

4 
6 
6 

7 

8 

9 
10 
11 

12 

A389BrAgLb    &.... 
A499BrAgLb    T£  
A1688                 86-6.. 

A511W          jg  

1 

2W.R 
R 

AA83           A. 

1 
2 
1 
3 

2 
3 
5 
2 
2 

BrAgLb.BrAgTb 
BrAgTb  

....  Do 

A1690                 86-7.. 

Do  

3R 

B139                   8o-2.. 
Do  

M328B-Y  42-17.... 
20  W             BW  

3  SYAgLb  

SCrAgTb  

B141SCrAgLb8o-2.. 
Do  

M328B-Y  42-17.... 
20  W            BW  

356                4-toe  
393               4-toe  .... 
MllGSep    42-11.... 

Do  

1 

2 

2 

2 
2 

1 

3 

1 

3 
5 
3 

1 

SCrAgLb,  3  SY 
AgTb 
2  SCrAgLb,  SCr 
AgTb 

6  W 

M25                   9-1  ... 
M27a                  9-1  ... 
M82                    9-7... 

M92                   8o-4  .  . 

SCrAgLb,  BrY 
AgLb,  SYAgTb 

10  females.  .  .  . 

18 

30 

TABLES. 


133 


TABLE  71 — Continued. 


lOc.  Males  Aa. 

No. 

9  Non-Ag. 

^AgLb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 
2 
3 
4 

5 

6 
7 
8 
9 
10 
11 
12 

13 
14 

75               BB  .  .  .  . 
08  W          4-toe... 

A581 
L 

i 

? 

? 

~>0 

2 

3 

4 

BrAgLb 

4R.Y? 

09  W          4-toe... 

Do  

M7             &  

M133               8a-4... 
\  Do.. 

3 
2 

3 

SCrAgLb,  Sep 

/M7             &  
\AA58          jV  
M183         jV  

/ 
Do  

1 

1 

M261  Sep  7a-7.  .  . 

Do  

1 

87               fa.... 
S2                ,fo  .  .  .  . 

M201 
L 

>               8a-4  .  .  . 

2 

1 

Do.. 

4 

3 

R 

A1665         ,$g  

Do  

1 

2 

87,  A1665  ,fo  

Do  

3 

2R 

B137           lo-l  .  .  . 
/B133           ld-3... 
\B98             la-3.  .  . 
D148W      lc-8... 
5  males 

B155 

I         ] 

8o-l  .  .  . 

1 

2 

3o.. 

1 

7 

/'  ' 
D240  BCrAgLbl4-5.  . 

1 

1 

SCrAg,  Sep  

26 

33 

lOd.  Males  AA'. 

No. 

9  Non-Ag. 

^AsLb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

2 
3 
4 
5 
6 
7 
8 
9 

10 

11 
12 
13 
14 
15 
16 
17 
18 
19 
20 

31                       Mis 
M255                  lo- 
M253                  lo- 
M256                  la- 
M254,  M256      la- 
AA279                3a-; 
C22,  AA278       G.p 
B  9  9                  (ab< 
M168                 ^j. 

c  

M138  9-1  

? 

LO  

Do  

4 
4 
1 
1 
1 
4 

5 
3 
1 
2 
1 

LO  

Do  

LO  

Do  

LO  

Do  

.,  3a-3 

>ve)  .  . 

Do  
Do  

Do  

5 
3 

1 

1 

5 
2 

5 

4 
1 

M91     8a-4... 
}  Do.. 

SCrAgLb  

/M169                  3**    .      . 

/BrYAgLb,  2  BrCr 
I     AgTb 
SYAgTb  

1 

M171                  ^j 
M177                  Ic-S 
M86                   9-1 
M79  W              j>j  . 

/ 

Do  

' 

M210  15-14.. 

Do  

3 
2 
1 
4 
1 
5 
3 
1 

1 
3 
2 
2 
2 
4 
2 
3 

BrAgLb  

B31                     la- 
B53                    la-; 
B54                     la-] 
C29                    G.p 
B  9  9                  (alx 
M119                 jff. 

L  
\.  .    .. 

B121    86-2... 
Do  

L. 

Do    

Do  

>ve) 

Do  ... 

B130    8a-l... 
Do  

AA174                14-1  

5  males 

45 

50 

SUMMABT    OF    CBOSS    10. 


No. 

AgLb  (Aa  or  AA') 
tested  by  cross  with  Non- 
Ag'  (aa). 

Lb 

Tb 

Non 

10a 

7  females  Aa  

17 

20 

lOc 

5  males     Aa  

26 

33 

Total  

43 

53 

lOb 

10  females  AA'  

18 

30 

lOd 

5  males     AA'  

45 

50 

Total  

63 

80 

134 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  72. 
Cross  11. — Light-bellied  agoutis  (AA')  crossed  together. 

Both  parents  known  to  carry  recessive  ticked-belly  by  test  (except  in  the  case  of  AA533 
with  one  young). 

Expectation:  AA'  X  AA'  =  AA  +  2AA'  +  A'A'  (3  AgLb :  1  AgTb). 


No. 

9  AgLb. 

tfAgLb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

A1690                     8b-7  

M91  8a-4  

4 

2 

2 

M25                        9-1  

Do  

7 

3 

4  SYAgLb 

3 

M27a                      9-1  

Do  

6 

4 

M25,  M27a            9-1  

Do  

4 

6 

B139                       8a-2  

Do  

1 

6 

M25,  M27,  B139   

Do  

1 

3 

BYAgTb  

7 

AA533                     11-1  

Do  

1 

8 

AA588                    11-2  

Do  

2 

1 

SYAgTb  

Total  

7!5 

q 

TABLE  73. 
Cross  12. — Miscellaneous  matings  of  ticked-bellied  agouti  with  ticked-bellied  agouti. 


No. 

9  AgTb. 

cfAgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

AA203  BrCrAgTb  2-5. 

AA16                     g'j  .  .  . 

8 

1 

SCrAgTb, 

W 

2 

M19                         2-16... 

Do  

3 

LBr 

W 

3 

AA497  SYAgTb      10d-ll 

AA284                    12-7. 

1 

1 

LBr 

R 

4 

AA598                      3c-22  .  . 

Do  

2 

BrAgTb  .  .  . 

W 

5 

A1523                       g"j  

AA199  SCrAgTb  2-12  .  .  . 

3 

SCrAgTb.. 

6 

M203                        2-19  .  .  . 

AA284                    12-7... 

3 

2 

Sep  

7 

AA202                      2-7  

AA15                     &  

4 

2  SCrAgTb 

8 

AA206                      2-9  

AA177  SCrAgTb  lb-3  .  .  . 

7 

4  SCrAgTb 

9 

Do  

AA507                    3c-22  .  . 

1 

10 

AA342                      12-8.  .  . 

Do  

4 

11 

A1058                      fa  

M298                      15-16.. 

?, 

BrAgTb  .  .  . 

12 

AA242  SCrAgTb     12-8.  .  . 

Bl  17  SCrAgTb     ld-11.. 

1 

SCrAgTb  .  . 

TABLE  74. 
Cross  13. — Miscellaneous  matings  of  light-bellied  agouti  guinea-pig  with  non-agouti  hybrid. 


No. 

9  AgLb. 

cfNon-Ag. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

}3392                     G.p.... 

3 

1 

SCrAgLb  

1 

3444                     G.p.... 
01                         G.p.... 

JA1539            &  

fi 

1 

3R 

2 
3 

02                        G.p.... 
3256  BrY  AgLb  G.p.... 

JA426R(Br)  &..... 
A678  W         &  

7 

? 

7  BrCrAgLb,  2  LBr 

4 

3220  BrAgLb     G.p  

Do  

2 

2  BrAgLb  

5 

271  SAg(R)         G.p.  .  .  . 

M333Y        jfc  

4 

4  SCrAgLb  

6 

3a                        G.p.... 

M34  Sep        16c-l  .  . 

?, 

2  Sep  

7 

241  SAg(R)         ArF2.. 

M328  B-Y   42-17  .  . 

3 

3  SCrAgLb  

8 

299  SAg(R)      ArF2  .  . 

M156R         iV  

4 

3 

2  SAg(R)  

4  W 

9 

12,  16  SAg(R)     21-1  . 

M34  Sep        16c-l  .  . 

1 

2 

SCrAg,  Sep  

TABLES. 


135 


TABLE  75. 
Cross  14. — Miscellaneous  matings  of  light-bellied  with  ticked-bellied  agouti. 


No. 

9AgLb. 

c?AgTb. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

2 
3 
4 
5 

/20o,  5a            G.p  
\3015,3014      G.p  
20a,5a,3014  G.p  
AA173              14-1  .  .  . 
M82                  9-7.... 
49  9SAg(R)  ArF,... 

JA412  R(Br)            ^  

3 

1 

3R 

A1474                     &  

3 
1 

1 
1 

?, 

AA199  SCrAgTb  2-12  .  .  . 
A1161                     j1!  

SCrAgTb  .   . 

AA508                     3d-2  .  .  . 

13 

1 

4 

9  SCrAg,  BY 
AgTb 

TABLE  76. 
Cross  15. — Miscellaneous  crosses  involving  the  inheritance  of  agouti  in  rufescens  hybrids. 


No. 

9  Misc. 

cf  Misc. 

Lb 

Tb 

Non 

Remarks. 

Unclas- 
sified. 

1 

AA171  R                14-1.. 

AA1161  AgTbg^  

1 

R,  Cr 

2 

M137R                 9-1... 

AA286  AgTb    3c-4  .  . 

1 

3 

Do  

M29  Br              16-6  .  . 

? 

4 

MISlBrCrAgTb  15-15. 

C20  B               G.p.  .  . 

6 

6 

A1472  BrAgLb      &  

163B                 4-toe.. 

? 

6 

IA1562W                ^  

JAA83B             jfc  

4 

1 

8 

\A1688AgLb          86-6.  . 
f  M27a  AgLb           9-1  ... 

>393  B                 4-toe  .  . 

3 

R 

? 

9 

\M19  AgTb             2-16.. 
fM  175  AgLb           Sa-3.. 

JA1040B            t*ff  

1 

4 

10 

\AA242  SCrAgTb  12-8  .  . 
[M  195  AgLb           9-7... 

JM116Sep         42-11. 

1 

2 

11 

\M203  AgTb           2-19.  . 
fB  122  AgLb            86-2.. 

JC20  B               G.p  .  .  . 

?, 

2 

2 

1? 

\AA212  BrAgTb     2-6.  .  . 
FM92  AgLb             8a-l  .  . 

JA1513               5>j  

1 

2 

1 

BrAgTb  

2R 

13 

\M106Y?                 10c-2. 
[M85  R                    16-5.. 

JAA1161  AgTb  &  

1 

1 

BrAgLb  

W 

14 

\M82  AgLb               9-7  .  . 
[M56  AgLb              13-1  .  . 

JA1  170  AgTb     g^|  

1 

?! 

15 
16 

\M50AgTb             16-7.  . 
AA28  W                ^5  .... 

A1523  AgTb          s>j  

A1513  AgTb    s'j  .  .  .  . 
M83AgLb        9-7... 

2 
1 

3 
1 

BrAgLb,  SCrAg 
Tb,  BrCrAg 
Tb 

R,2Cr 

17 

A1413B                 ,&  

Do  

2 

18 

M84  R(Br)             16-5  .  . 

A1161AgTb     fc  

W 

19 

fA556AgLb            ^  
JA587W                  &  

[104B                4-toe.. 

2 

3 

[A533Y                   &  
/A495AgLb            -tV  

1 

3R 

20 

\A867B                   ^  
/AA621SYALb      11-2.. 

>163  B                4-toe.. 
BW36  W  BW... 

1 

SCrAgTb  

21 

\AA621  SYALb      

724  SAg(R)      lea  ... 

3 

SSYAgTb  

22 
?3 

399SAg(R)        ArF2.. 
198W                      ArF2  .  . 

M224  BrAgLb  9-2... 
M291  B            &  

21 
1 

1 

10  SAg(R),  SAg 
Tb(R) 

W 

24 

29  9  W                 ArF2.  . 

M2B                 j^g  

?, 

1 

3  W 

28 

D125  W                  la-13 

133  SAg(R)       24-1  .  . 

1 

1 

SAg(R),Sep(R). 

26 

D427W                  la-14. 

133  SAg(R) 

1 

1 

SAgTb(R),  Sep 

27 

D86  W                   76-3  .  . 

126  BWAg(R)  24-2  .  . 

?, 

3 

(R) 
2  SAg(R),  3  Sep 

(R) 

136 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  77. 

Cross  16. — Matings  of  dilute  with  albino  of  intense  stock. 
Expectation:  CaCd  X  CaCa  =  CdCa  (all  Dil). 

CdCr  X  CaCa  =  CdCa  +  CrCa  (1  Dil :  1  RE). 
CdCa  X  CaCa  =  CdCa  +  CaCa  (1  Dil :  1  W). 


16o.  Females  CdCd- 

No. 

9  DU. 

cTW  (intense  stock). 

Int 

Dil 

RE 

W 

Remarks. 

1 
2 
3 

4 

AA621S3YjAg       39-4  
58  Seps                   Dil  .    .    . 

BW36  W               BW  

1 

SjCrjAgTb 
2Seps 
2  Seps,  Sepr-Cr* 
3  SsCr»AgTb 

75  W                      BW  .  . 

? 

Do  

20  W                     BW... 

3 

Do  . 

B42  W                   la-3     . 

3 

Total 



9 



' 

166.  Females  CdCa. 

No. 

9  Dil. 

cf  W  (intense  stock). 

Int 

Dil 

RE 

W 

Remarks. 

1 

2 
3 
4 

5 

6 

7 
8 

9 

10 
11 
12 
12a 
13 
14 
15 
16 

15  Sep«                   Dil  
17  Cr»                     Dil  

75  W                      BW.... 
B42  W                   la-3  .  .  . 

4 
1 

3 

2  Seps,  2  Sep4 
Sepe 

30  Cr»                     Dil  

Do  

2 

55  Cr6(Br)              Dil  

Do  

1 

1 
4 

SjCrjAgTb 
8Sep6 

3Sep4 
Sep4 
SjY^SsCrjAg 
Sep4 
SiCrsAgTb,  2  S, 
Y4Ag 

Seps-Oi 
Sep3,  S3O6Ag 

Sepj,  2  Sep4 
Sep4,  Sep6 
Seps 

/M42LBr                42-12... 
\M44Crs                 42-12... 
M42  LBr               42-12... 

J15W                     BW.... 
Do  

8 
3 

AA600  LBr-Crs     39-19  .  .  . 

Do  

1 

M357  S4CrsAg       42-1  .... 
B141  S4Y4Ag         39-23... 

20  W                      BW.... 

Do  

3 
3 

3 

6 

4 
1 
2 
2 
2 
1 

D43,  D44  Sep3       16o-3  .  .  . 

Do  

D45  Sj-Crj             16a-3  .  .  . 

.    ..Do  

1 

D95  S3Y4Ag           166-9  .  .  . 
D95,  M357             

20  W                      BW.... 

Do  

? 

D67  S3-Cr6             16&-4  .  .  . 

...  Do  

M384Seps             39-12... 
M442  BrCrjAgTb  39-12  .    . 

86  W                     BW.... 
.Do  

3 
? 

D66  Ss-Crj             406-13  .  . 

.      .Do  

1 

1 
32 

Total 



33 



16c.  Males  CdCa. 

No. 

9W. 

cfDil. 

Int 

Dil 

RE 

W 

Remarks. 

1 
2 
3 
4 

5 
6 

132  W                     4-toe.... 
12oW                     4-toe.... 
5W                         BW  

A674  Sepe             i  

4 

3  Sep4-Cr6,  Sep 
3  Sep8-Cr« 
2Sep6 
Ss-Crj,  SjCrjAg 
Tb 
2  SsCr6AgTb 
Sep4 
2  SjYiAg,  3  S4- 
Y4,  2  S4,  S» 

M34  Sep8-Crs       16c-l  .  . 

3 

Do  

2 

1 
5 

82  W                       BW  

/BW11W               BW  
\BW15W               BW  
120,  21,  23,  29  W    22-  

Total 

B117  S4CrsAgTb  39-14.  . 
\  Do.. 

2 
3 

/ 
13Cr,(Br)            Dil  

8 

13 
19 



99 



TABLES. 


137 


SIMILAR  MATINQS  FROM  CROSSES  19,  27,  AND  33,  AND  SUMMARY  OF  CROSS  16. 


No. 

Dilute. 

W  (intense 
stock). 

Int 

Dil 

RE 

W 

5  9  9  Dil   (CdCr)  

W     BW.... 

9 

10 

3  o*  d"  Dil  (CdCr)  

.  ..Do  

8 

5 

7  9  9  Dil  (CdCa)  .... 

.  ..Do  

5 

7 

1  cf      Dil  (CdCa)  

...  Do  

4 

?, 

16o 

9  9  Dil  (CdCd)  .... 

W     

q 

166 

9  9  Dil  (CdCa)  .... 

.  .  .Do  

33 

3?, 

16c 

d"  cf  DU  (CdCa)  .  .  . 

.     Do  

?,?, 

19 

Total  

85 

15 

60 

TABLE  78. 

Cross  17. — Matings  of  intense  from  intense  stock  with  albinos  from  dilute  stock  or  from 

two  dilute  parents. 

Expectation:  CC  X  CaCa  =  CCa  (all  Int). 

CCa  X  CaCa  =  CCa  +  CaCa  (1  Int :  1  W). 


17o.  Male  CC. 

No. 

9W. 

cflnt. 

Int 

Dil 

RE 

W 

Remarks 

1 

M117  W  42-11  

3013  B  BB  

2 

2B 

2 

M327  W  42-17  

Do  

?, 

2B 

3 

D  37   W  Dil  

Do  

?, 

2B 

Total  

6 

17&.  Female  CC. 

No. 

9  Int. 

cTW. 

Int 

Dil 

RE 

W 

Remarks. 

1 

22,  23,  33  Ag  Misc  

11  W     Dil 

11 

11  Ag 

2 

CIS,  C50  Ag  Misc  

Do  

ft 

6B 

3 

(C24  Ag          Misc  

\  Do.. 

4 

Ag,  3B 

4 

\C34  B            Misc  
22  Br              Misc  

/ 

...     Do 

4 

4Br 

/S22B              ,*,.. 

6 

}M313  W  42-16.  . 

4 

4B 

7 

3223  B            Misc  

J 

Do  

? 

2B 

8 

B232  B           ld-21  

M201  W  42-13 

2 

2B 

9 

B23AgTb      ld-12  

Do  

1 

AgTb 

Total  

34 

17c.  MaleCCa. 

No. 

9W. 

9  Int. 

Int 

Dil 

RE 

W 

Remarks. 

1 

D37  W  Dil  

06  B  BW  

?, 

2B 

2 

9  W       Dil  

Do  

1 

fl 

B 

Total  

3 

9 

138 


INHERITANCE   IN   GUINEA-PIGS. 
TABLE  78 — Continued. 


17d.  Female  CCa. 

No. 

9  Int. 

cfW. 

Int 

Dil 

RE 

W 

Remarks. 

1 

D48  Ag               176-1  

11  W       Misc  

2 

2 

D49  Ag                176-1  

Do  

1 

2 

Br. 

3 

D224  Ag              176-1  

Do  

1 

1 

R 

3o 

D224,  D226  Ag  176-1  

Do  

3 

2 

Ag,  2B 

4 

B33  AgTb           ld-18  

M201  W  42-13  

2 

1 

2  AgTb 

5 

B52  AgTb           la-3  

Do  

2 

2  AgTb 

6 

BllOAgTb         la-1  

Do  

1 

7 

Bill  AgTb         la-1  

Do  

3 

1 

AgTb,  2  B 

8 

B128  AgTb         la-1  

Do  

1 

AgTb 

Total  

13 

10 

SUMMARY  OF  CROSS  17. 


No. 

Intense 
(intense  stock). 

White 
(dilute  stock)  . 

Int 

Dil 

RE 

W 

17a 

cf  cflnt  CC.... 

W  

6 

176 

9  9  Int  CC...  . 

Do  

34 

17c 

d"d"Int  CCa.  • 

Do  

3 

2 

17d 

9  9  Int  CCa  •  • 

Do  

13 

10 

Total  .  .  . 

56 

12 

TABLE  79. 

Cross  18. — Intense  guinea-pigs,  each  of  which  had  a  dilute  parent  known  to  transmit 
albinism,  mated  with  albinos  or  red-eyes  to  test  whether  the  same  intense  animal  can 
transmit  both  dilution  and  albinism. 
Expectation:  CCa  X  CraCra  =  CCra  +  CaCra  (1  Int :  1  Dil). 

CCa  X  CraCra  =  CCra  +  CaCra  (1  Int :  1  RE  or  W). 


18o.  Male  CCd  by  test. 

No. 

9  Red-eye. 

cflnt. 

Int 

Dil 

RE 

W 

Remarks. 

1 
2 
3 

4 
5 

6 

7 
8 

9 
10 

515SAg(R)           ArF2.. 
774  SAg  (R)           ArF2.. 

D  10  R  (Br)      35-1  .  .  . 
Do  

3 
1 

3 

3  Ag.SCrAg,  2  S3Y«Ag 
Ag 
3  Ag,2  S!iY4Ag,  S4Cr6 
Ag 
4  B,2  Si-Crs,  S4-Y4 
3  Ag.SsY^Ag,  S4Y4Ag 
S6Cr6Ag,  2  SiYiAg 
2    S4Cr5Ag,    S6Cr, 
Ag 
3  Ag,2  S3Y4Ag,  S6Y4 
Ag 
2  B,S3Cr5Ag 
3  Ag,BiY4AgTb,  S3CrB 
Ag 
Ag.SsY^g,  SjY^g 
4  S4Cr5Ag,  S«Cr6 
Ag 
2B^ 

515,  774  SAg  (R)   ArF2.. 

Do  

3 

4 
3 

3 

2 
3 

1 
2 

3 

3 

8 

3 

1 
2 

7 

514Sep(R)            ArF2.. 

...    .Do  

281  SAg  (R)           ArF2.. 
741  SAg  (R)           ArF2.. 

D  30  R  (Br)      36-1  .  .  . 
Do  

241  SAg  (R)           ArF2.. 
413  SAg  (R)           ArF2.. 

AA508AgTb    3d-2... 
Do  

759  SAg  (R)           ArF2.. 

Do  

M430  SAg  (R)        18r-4  . 
Total  3  males 

Do  

25 

30 





TABLES. 

TABLE  79 — Continued. 


139 


186.  Female  CCd  by  test. 

No. 

9  Int. 

C?  Red-eye  or  W. 

Int 

Dil 

RE 

W 

Remarks. 

1 

2 
3 

M292  B                   &  .  .  .  . 
M353  B                  A  

D  18  W             166-3  .  . 
Do  

2 

1 
2 

5 

3 

1 
1 

5 

AgTb,  B,S6Cr6AgTb, 
2Seps 
AgTb,Sep6 
(Cross  20) 

D6a  R  (Br)             35-1  .  . 
Total  3  females 

724  SAg  (R)      lea  





18c.  Male  CCa  by  test. 

No. 

9  Red-eye  or  W. 

cflnt. 

Int 

5 

91 

Dil 

RE 

3 
8 

W 

1 

Remarks. 

1 

2 
3 

4 
5 
6 

7 
8 
9 
10 
11 
12 
13 
14 
15 

271  SAg  (R)          ArF2.. 
278SAg(R)          ArF2.. 

M224  BrAg       406-12  . 
Do  

5Ag,2S4Ag(R),S7Ag 
(R) 
2Ag,5SAg(R) 
4Ag,S&Ag(R),SAg(R) 
SiAgTb  (R) 
2  Ag,  3  B,2  SAg  (R) 

AgTb.SgAgTb  (R) 
Seps  (R) 
2  AgTb,Sep4  (R) 
4B,Sep6(R),2Sep(R) 
2  Ag,SeP4  (R) 
Ag,  B 

2  Br,  Ag 
5B,  Ag 
11  B 

2  Ag,  8  B 

716  SAg  (R)           ArF2.. 

Do  

4 

3 

233  SAg  (R)          ArF2.. 
773  SAg  (R)          ArF2  .  . 

M156R(B)      ^  
Do  

5 

2 

3 
1 
1 

236Sep(R)           ArF2.. 
264  Sep  (R)            ArF2 

AA433aAgTb  36-4... 
Do 

1 
2 

2 
1 

485Sep(R)            ArF2.. 
235  Sep  (R)           ArF2.. 
693  W                      ArF2.. 

D7  R  (Br)         35-1  .  .  . 
D13  R  (Br)       35-1  .  .  . 
Do  

4 

2 

a 

3 

1 

1 
2 
3 

9 
13 

7 

41 

D42  W                    166-1  . 
AA578  W               3c-18  . 
3  9  9  W               ArF2.. 
4  9  9  W                Misc.  . 
3  9  9  W               ArF2.. 

Total,  8  males 

Do  

Do  
M291  B             ^j 

3 

6 

M339  B             40o-14  . 
M2B                  i>g  

11 
10 

57 



20 

140 


INHERITANCE   IN    GUINEA-PIGS. 


TABLE  80. 
Cross  19. — Matings  of  dilute  from  cross  18o  or  43,  with  albino. 

Expectation:  CdCr  X  CaCa  =  CdCa  +  CrCa  (1  Dil :  1  RE)  (1-6). 
CdCa  X  CaCa  =  CdCa  +  CaCa  (1  Dil :  1  W)  (7-13). 


No. 

9  Dil  (or  W). 

cfW  (or  Dil). 

Int 

Dil 

1 
1 
2 

RE 

W 

Remarks. 

1 
2 
3 

4 
5 
6 

7 
8 

9 

10 
11 
12 
13 
14 

D72S3Y4Ag      18a-5.. 
D63  S4Y4Ag     43-2  .  .  . 

BW36W         BW  ... 

2 
3 
2 

?: 

Sr-Y4,StAg(R),Sept(R) 

Sep4,  2  SjAg  (R),  Sep4  (R) 
SaCrsAg,  SrOi,  SsAg(R) 
Sepa  (R) 
SsAg(R),  Sep»(R) 
S4Ci5Ag,  Sep4 
2  S5Cr6Ag,  Sj-Cre,  S^g 
(R) 

S,Y4Ag 
2  S4CrsAg,  Sep4 

S4O(Ag 
3  S4CrftAg 
SsY^g,  S4-Cr6 
3  S.Y.Ag 
Sepe 

Do  

D121W            18o-9.. 
157  W                22-3... 

D71  SsOiAg  18o-5.  . 

Do  

D148W            lc-8... 
D239W            18c-6.. 

D240  SjY^g  18o-9  .  . 

2 

Do  

3 

1 

DGlSsY^Ag     43-2... 
D241S6CrsAg  18o-9.. 
/D69S4Cr&Ag   18o-5.. 
\M425SYAg    43-1... 
S772W             ArF2... 
256  W               ArF2... 

BW36W         BW.... 

1 
1 

1 

BW50W         BW.... 
JBW36  W        BW.  .  .  . 
D70S4Y4Ag    18a-5.. 

1 
3 
1 

Do  

3 

3 

1 

S781W             ArF2... 

Do  

? 

D69S4Cr6Ag    18o-5.. 
D206S4-Y4      18a-4.. 

2  females  CdCr 

BW36W         BW.... 

T 

BW50W         BW.... 

1 



2 
7 
?, 

5 
5 

3 

4 

2  males  CdCr  

3  females  CdCa  

1  male  CdCa  

6 

2  females  (?)  

fi 

TABLE  81. 

Cross  20. — Matings  of  pure  lea  male  724  CrCr. 
Expectation:  CC  X  CrCr  =  CCr  (all  Int)  (1). 

CCd  X  Q-Cr  =  CCr  +  CdCr  (1  Int :  1  Dil)    (2-3). 

CdCd  X  CrCr  =  CdCr  (aU  Dil)  (4-5). 

CdCa  X  CrCr  =  CdCr  +  CrCa  (1  DU :  1  RE)    (6). 


No. 

9  Misc. 

cf  Red-eye  lea. 

Int 

Dil 

RE 

W 

Remarks. 

1 
2 
3 
4 
5 
6 

5  9  9  B                  Trior4-toe 
D6aR(Br)              35-1   .    .    . 

724SAg(R)  lea... 

q 

9Ag 
2  Ag,  SzY4Ag 
Ag 
2S2Y4Ag 
SSjY^g 
BiCr&Ag,  S<Ag(R) 

...  Do 

2 
1 

1 

D209  R(Br)             36-3  

Do  

AA606  SjYsAgTb   40o-8  

Do  

? 

AA621  SsY2Ag        39-4  

Do  

3 

SA61  Sep4               32-2  

Do  

1 

1 

TABLE  82. 

Cross  21. — Matings  of  pure  lea  male  575 
Expectation:  CCr  X  CaCa  =  CCa  +  CrCa  (1  Int :  1  RE). 


No. 

9W. 

cf  Int  lea. 

Int 

Dil 

RE 

W 

Remarks. 

1 

5  9  9  W    BW  

575  Ag     lea.  . 

9 

4 

4  Ag,  5  B,  2  S4Ag(R),  2  Sep4(R) 

TABLES. 


141 


TABLE  83. 

Cross  22. — Matings  of  intense  Fi  lea  (cross  21)  with  albinos. 
Expectation:  CCa  X  CaCa  =  CCa  +  CaCa  (1  Int :  1  W). 


No. 

9  W  (or  Int.  Fi  lea. 

d"Int  Fi  lea 
(or  W). 

Int 

Dil 

RE 

W 

Remarks. 

1 

2  9  9  W    BW  .   .. 

13  Ag  21-1  .  .  . 

4 

3 

4B 

2 

141  W         ArFj. 

Do  

4 

3 

M79  W       /,  

14  B     21-1  .  .  . 

2 

4 

2B 

4 

D17  W        166-3  .  .  . 

Do  

? 

ft 

19  Ag          21-1  

d"  W   BW.... 

2 

? 

2B 

ft 

111  Ag        21-1  

Do  

4 

4 

Ag,  3B 

7 

17  B            21-1  

Do  

4 

6 

4B 

Total  

16 

?5 

TABLE  84. 

Cross  23. — Matings  of  red-eye  Fi  lea  (cross  21)  with  albinos  of  intense  stock. 
Expectation:  CVCa  X  CaCa  =  CrCa  +  CaCa  (1  RE :  1  W). 


No. 

9  White. 

c?  Red-eye  Fj  lea. 

Int 

Dil 

RE 

3 

W 

Remarks. 

1 

8W     BW.... 

15  Sep4(R)     21-1  

3  Sep3(R) 

TABLE  85. 

Cross  24- — F2  from  red-eye  Fi  lea  (cross  21). 
Expectation:  CrCa  X  CVCa  =  CrQ.  +  2  CrCa  +  CaCa  (3  RE :  1  W). 


No. 

9  Red-eye  Ft  lea. 

cfRed-eye  FI  lea. 

Int 

Dil 

RE 

W 

Remarks. 

1 

12  S4Ag(R)    21-1 

15  Sep4(R)    21-1  .  . 

5 

5 

(82,  Ss,  S5)  Ag  (R),  S4(R),  85 

2 

16  S4Ag(R)    21-1 

.      .Do        

1? 

1 

(R) 

(B0,  3  82,  83,  S«)  Ag  (R)  ;  (B0, 

Sz,  2S4,  Si,  Se)(R) 

TABLE  86. 

Cross  25. — Matings  of  F2  lea  (cross  24)  with  albinos. 
Expectation:  CrCr  X  CaCa  =  CrCa  (all  RE)  (1-7). 

CrCa  X  CaCa  =  CrCa  +  CaCa  (1  RE  :  1  W)    (8-9). 


No. 

9  White. 

C?  Red-eye  F2  lea. 

Int 

Dil 

RE 

W 

Remarks. 

1 
2 

3 

3a 
4 
5 
6 
7 
8 
9 

D86W           43-3.... 
M431  W         18c-4... 

126  BoWAg(R)  24-2  .  . 

5 

S4Ag(R),S6Ag(R),8, 
(R),  2  S6(R) 
3S4Ag(R),2S6Ag(R), 
Sep4(R) 
2S8(R),3S6(R) 
83,  S4,  85,  Se 
3  S6(R),  2  Se(R) 
S6Ag(R),  S.(R) 
S6(R) 
SeAgTMR),  S«(R) 
3  S4(R) 

Do  

6 

D76,  D78W18c-14.. 
D76  W           18c-14  .  . 

137  B0(R)            24-2  .  . 

5 

Do  

4 

D77  W           18c-14  .  . 

Do  

6 

D125W         16c-4... 
BW48W        BW  

133  &2Ag(R)        24-1  .  . 

? 

Do  

1 

D427  W         44-3   .  .  . 

Do  

2 

D73  W           42-6  
8755  W          ArF2.    .. 

134  Sep4(R)        24-1  .  . 

3 

2 
1 

Do  

142 


INHERITANCE   IN   GUINEA-PIGS. 

TABLE  87. 
Cross  26.  —  Matings  of  red-eye  F!  lea  (cross  21)  with  dilute. 


Expectation:  CdCd  X  CrCa  =  CdCr  +  CdCa  (all  Dil). 

CdCa  X  CrCa  =  CdCr  X  CdCa  +  CrCa  +  CaCa  (2  Dil  :  1  RE  :  1  W). 


No. 

9  Dil  (or  Red-eye  FI  lea. 

cf  Red-eye  FI  lea 
(or  Dil). 

Int 

Dil 
3 

RE 

W 

Remarks. 

1 

2 

3 

4 

AA242  S8Y3AgTb   40a-6.. 

/AA244  Sep4              39-15  .  . 
\M261Sep4               41-2... 

12  S4Ag(R)               21-1  ... 
16  S4Ag(R)               21-1  .  .  . 

15  Sep4(R)         21-1  .  .  . 

BiCrjAgTb,  Bi- 
Os,  Seps 
f5Bi,S4,Ss-Crt,S,, 
SS(R),2S4(R), 
I     8,(R) 

s, 

S7Cr6Ag,  Sr-Crj 

1  Do  .  . 

8 
1 

4 

5 

/ 

M34  Sep«-CrB  16e-l  .  . 

Do  

2 

TABLE  88. 
Cross  27. — Matings  of  dilute  from  cross  26  with  albinos. 

Expectation:  CdCr  X  CaCa  =  CdCa  +  CrCa  (1  Dil:  1  RE)  (1-6). 
CdCa  X  CaCa  =  CdCa  +  CaCa  (1  Dil :  1  W)  (8-12). 


No. 

9W  (or  Dil). 

d"Dil  (or  W). 

Int 

Dil 

RE 

W 

Remarks. 

1 

3  9  9  W           Misc..  . 

D89  Sep8                 26-3  .  . 

4 

ft 

2  S4,  S6-Y4,  Sj-Cre, 

?, 

D221  W             3>2  

D196Bi                   26-2.. 

1 

2  S6(R),  S,(R),  2 
S7(R).  S8(R) 

Sj 

3 

G30  W               St  

Do  

1 

3 

S6,  S4(R),S6(R),87 

4 

D115Bi-Cr6      26-1... 

BW50                     BW    . 

3 

(R) 
3  S3(R) 

5 

D197Bi              26-2... 

JBW46                     BW 

3 

? 

3  S4,  2  S6(R) 

6 

7 

D198Bt              26-2... 
BW43  W            BW  . 

DllSBiOsAgTb  26-1 

?, 

S4,  Ss-CrsAgTb 

8 
9 
10 
11 

482  W                 ArF2... 
D42  W                166-1  .  . 
BW56.57           BW.... 
D122  SrCrsAg    26-4 

D123Si-Cr6           26-4.. 
D55S5-Cr5             26-2.. 
D114Sep6               26-1.. 
BW50                      BW 

3 

4 
4 

1 
3 
2 
? 

S6,  2  S6-Y4 
85,  Sc,  S4,  Se—  Cre 
2  S4,  2  S4-Y4 

12 

D195  Sep  4          26-2 

Do 

1 

1 

S< 

TABLE  89. 
Cross  28. — Matings  of  pure  Arequipa  male  1007  CdCd  with  black  guinea-pigs. 

Expectation:  CC    X  CdCd  =  CCd  (all  Int). 

CCa  X  CdCd  =  CCd  +  CdCft  (1  Int  :  1  Dil). 


No. 

9  Intense. 

cf  Dilute  (Arequipa). 

Int 

Dil 

RE 

W 

Remarks. 

1 

2  9  9  B  4-toe  

^007  SYAg  .... 

4 

3Ag,  B 

2 

49  9B  BW  

...     Do 

10 

5Ag,  5B 

3 

1442  B    BW  

Do 

3 

2 

2  Ag,  B,  SCrAg,  Sepi 

'1007  SYAg  CdCd  from  1001  BRAg  CCd  and  1002  SCrAg  CdCr  pure  Arequipa  stock. 


TABLES. 


143 


TABLE  90. 

Cross  29. — Matings  of  intense  FI  (cross  28)  with  of  1007. 
Expectation:  CCd  X  CdCd  =  CCd  +  CdCd  (1  Int :  1  Dil). 


No. 

9  Intense  ArFi. 

c?  Dilute  (Arequipa). 

Int 

Dil 

RE 

W 

Remarks. 

1 

SA4  Ag      28-3  .... 

4007  SYAg 

3 

2Ag,  R 

2 

SA8  Ag      28-2  

..Do.  . 

9 

2 

AR,  R,  Bi-Yj,  Ys 

(SA4,  SA8   

\                  T^ 

3 

>  Do  

3 

2 

2  Ag,  B,  BiYsAg,  Y3 

\SA10  B      28-2  

/ 

J1007  SYAg  CdCd  from  1001  BRAg  CCd  and  1002  SCrAg  CdCr  pure  Arequipa  stock. 

TABLE  91. 

Cross  SO.— Mating  of  dilute  FI  (cross  28)  with  c?  1007. 
Expectation:  CdCa  X  CdCd  +  CdCd  +  CdCa  (aU  Dil). 


No. 

9  Dilute  ArFi. 

9  Intense  (Arequipa). 

Int 

Dil 

RE 

W 

Remarks. 

1 

SA3  Sep3  28-3 

r1007  SYAg 

2 

BiY»Ag,  Y! 

J1007  SYAg  CdCd  from  1001  BRAg  CCd  and  1002  SCrAg  CdCr  pure  Arequipa  stock. 

TABLE  92. 

Cross  31. — Fs  from  intense  FI  Arequipa  (cross  28). 
Expectation:  CCd  X  CCd  =  CC  +  2  CCd  +  CdCd  (3  Int :  1  Dil). 


No. 

9  Intense  ArFi. 

cT  Intense  ArFi. 

Int 

Dil 

RE 

W 

Remarks. 

f  SAG  B     28-2  

1 

>SA2  B     28-2  

17 

3 

17  B,  2  B-Ys,  Bj-Y« 

\SA1  1  B  28-2  

2 

SA13  B  28-3  .... 

SA7Ag  28-2. 

1 

B                   fS'  --.  =  •. 

3 

fSASAg  28-2  

\  Do  .  . 

3 

Ag,  2B 

4 

\SA10  B  28-2  

SASAg  28-2 

/ 
Do 

1 

2 

Ag,  B2Y»Ag,  Br-Ys 

5 

SA4  Ag  28-3  

Do  

1 

91 

Ag,  2  B!Y»Ag 

Total  

?3 

7 

TABLE  93. 

Cross  82.— F2  from  dilute  Fj  X  intense  Fi  (cross  28). 
Expectation:  CdCa  X  CCd  =  CCd  +  CCa  +  CdCd  +  CdCa  (2  Int :  2  Dil). 


No. 

9  Dil  ArFL 

d"Int  ArFi. 

Int 

Dil 

RE 

W 

Remarks. 

1 

SA3  Sepa  28-3  

SA7  Ag    28-2  

1 

1 

B,  B2Y3Ag 

2 

Do  

SA12  Ag  28-3  

1 

1 

B,  84 

144  INHERITANCE   IN   GUINEA-PIGS. 

TABLE  94. 

Cross  33. — Mating  of  dilute  FI  Arequipa  with  albino. 
Expectation:  CaCa  X  CaCa  =  CaCa  +  CaCa  (1  Dil:  1  W). 


No. 

9  Dil  ArF,. 

d"  White. 

Int 

Dil 

RE 

W 

Remarks. 

1 

SA3  Sepa  28-3  ...          .... 

75  W  BW           

1 

TABLE  95. 

Cross  34. — Matings  of  intense  Ft  Arequipa  with  albinos. 
Expectation:  CCd  X  CaCa  =  CCa  +  CdCa  (1  Int :  1  Dil). 


No. 

9  Int  ArF!  (or  W). 

cfW(orlntArFi). 

Int 

Dil 

RE 

W 

Remarks. 

1 

SA4  Ag              28-3   .  . 

M313W  42-16. 

? 

2  Y4 

2 

SA10,  11,  13  B  28-2,  3 

.  Do  .  .      . 

4 

R 

3  B,  R,  2  Ss,  4  Ss-Cn.  2  Y4 

3 

149  W                 22-2  .... 

SA26  Ag  28-1.  .  . 

8 

?, 

2  Ag,  B,  SaYiAg,  SjCrjAg 

4 

161  W                 24-1  .... 

Do  

3 

1 

2  Ag,  B,  82 

5 

349  W                ArF2  

Do  

1 

1 

Ag,  83 

6 

149,  349  W         

Do  

2 

6 

Ag,  B.SsCrsAg,  2  S6YtAg, 

2  SsCrsAg,  S3-Crj 

Total  .     .    . 

13 

?n 

TABLE  96. 

Cross  85. — Mating  of  cream  of  dilute  selection  stock  with  a  red  stock  free  from  albinism  or 

dilution. 

Expectation:  CC  X  CdCa  =  CCd  +  CCa  (all  Int). 


No. 

9  Intense. 

cf  Dilute. 

Int 

Dil 

RE 

W 

Remarks. 

1 

499  R(Br)  Misc. 

00  Cr6(Br)  Dil  

12 

11  R(Br),  Y2(Br) 

TABLE  97. 
Cross  36.  —  FI  (cross  35)  mated  with  father. 


Expectation:  CCd  X  CdCa  =  CCd  +  CCa  +  CdCd  +  CdCa  (2  Int  :  2  Dil)  (3). 

CCa  X  CdCa  =  CCd  +  CCa  +  CdCa  +  CaCa  (2  Int  :  1  Dil  :  1  W)  (1-2). 


No. 

9  Intense  FI. 

cf  Dilute. 

Int 

Dil 

RE 

W 

Remarks. 

1 

2 

Dl  R(Br)       35-1  
D2  R(Br)       35-1  

OOCr6(Br)Dil... 
Do  

4 

6 
1 

2 
1 

4  R(Br),  2  Y4(Br),  4  Cr8(Br) 
Cr6(Br) 

3 

D6  R(Br)       35-1 

Do 

s 

4 

3  R(Br),  Y2(Br),  3  CrB(Br) 

4 

D136  R(Br)  36-1 

Do 

9 

1 

2  R(Br},  Cr6(Br) 

- 

TABLES. 
TABLE  98. 


145 


Cross  37. — Matings  of  dilute  with  dilute  in  the  dilute-selection  stock. 

Expectation:  CdCd  X  CdCd  =  CdCd  (all  Dil). 

CdCd  X  CdCa  =  CdCd  +  CdCa  (all  Dil)  (1). 

CdCd  X  CdCa  =  CdCd  +  2  CdCa  +  CaCa  (3  Dil :  1  W)  (2-11). 


No. 

9  Dilute. 

c?  Dilute. 

Int 

Dil 

RE 

W 

Remarks. 

1 

D301  Y4                     Dil  .... 

D292Y4          Dil... 

3 

Y3,  2  Cr6 

2 

Do  

D298  Cr6         Dil 

2 

Y8,  Crs 

3 

D300  Cr6                     Dil  .... 

Do  

3 

1 

Y3,  2  Cr6 

4 

D299Cr«                     Dil  

Do  

5 

Y4,  3  Cr6,  Cr» 

5 
6 

D289Cr«                    Dil.... 
D291Cr6                     Dil  

D290Cr«         Dil... 
Do  

6 

1 
2 

Y3,  4  Cr6,  Cr« 

7 
8 

/D260Y3(Br)               Dil.... 
\D262,  D263  Cr6(Br)  Dil.  ... 
D263Crg(Br)              Dil.... 

JD261Cr6(Br)Dil... 
Do  ... 

4 
3 

1 

2 

Y8(Br),3Cr6(Br) 
Y3(Br),2Cr6Br 

9 

D262Cr6(Br)              Dil  

Do  . 

3 

2 

Y3(Br),  CrB(Br), 

10 

[D265  Cr6(Br)               37-7.. 

1  Do.  . 

4 

Cr6(Br) 
Y3(Br),3Cr6(Br) 

11 

\D266  Cre(Br)               37-7  .  . 
D265                             37-7  .  . 

/ 
Do  .    . 

2 

1 

Y3(Br),  Cr6(Br) 

Total  (excluding  1)  .  . 

32 

10 

TABLE  99. 
Cross  38. — Matings  of  dilute  with  albino  in  the  dilute-selection  stock. 

Expectation:  CdCd  X  CdCa  =  CdCa  (all  Dil). 

CdCa  X  CaCa  =  CdCa  +  CaCa  (1  Dil :  1  W). 


No. 

9  White  (or  Dilute). 

d"  Dilute  (or  W). 

Int 

Dil 

RE 

W 

Remarks. 

1 

38a. 
D293  W           Dil 

D292  Y4           Dil 

4 

4Crs 

2 

D294  W           Dil 

Do 

2 

2Cr6 

3 

D264  Y3(Br)  37-7  

11  W                 Dil  

?, 

2  Cr»(Br) 

2CdCd  

8 

1 

386. 
D293  W           Dil 

D290  Cr«          Dil 

2 

2Cr4 

2 

D302  W           Dil  

D298  Cr5          Dil  

1 

Cr6 

3 

D303  W           Dil  

.  .Do  

2 

2Cr5 

4 

D  75  W           Dil  

D267  Cr6(Br)  37-7  

4 

5 

Do  

D274  Cr6(Br)  Dil  

?, 

1 

2  Cr6(Br) 

fD276  W           Dil  

6 

>D261  Cr6(Br)  Dil  

3 

2 

3  Cr«(Br) 

\D272  W           Dil      .    ... 

5  CdCa      . 

10 

7 

146 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  100. 

Cross  89. — All  matings  of  intense  with  intense  which  have  given  dilute  young,  except  those 

given  in  cross  31. 

Expectation:  CCd  X  CCd  =  CC  +  2  CCd  +  CdCd  (3  Int :  1  Dil)  (1-7). 

CCd  X  CCa  =  CC  +  CCd  +  CCa  +  CdCa  (3  Int :  1  Dil)  (8-33). 
3,  9,  11,  24,  26,  30,  and  32  not  wholly  certain. 


No. 

9  Intense. 

d"  Intense. 

Int 

Dil 

RE 

W 

Remarks. 

1 

M353  B             ^j  

SA26  Ag          28-1  .  .  . 

3 

1 

Ag,  B,  R,  Sj-Yj 

2 

A780  AgTb        fa  

A781  AgTb     fa  

7 

2 

4  AgTb,  3  R,  BrYAg 

3 

B58  AgTb          ld-15  .  . 

B  118  AgTb     ld-6... 

9 

2 

Tb,  Y 
5  AgTb,  3  BrAgTb, 

4 

M25  AgLb         9-1  

M91  AgLb      8-4  

6 

4 

B,  SjYjAgTb,  St 
3  Ag,  3AgTb,  2  SYAg 

5 

AA588  Ag          39-4  .  .  . 

.Do       

2 

1 

Lb,  2  S3Y2AgLb 
2  Ag,  S3YsAgTb 

6 

f  M25,  M27a  Ag  9-1  .... 

>       .Do 

3 

1 

[Ag,  2  AgTb,  BiYiAg 

7 

\B139  Ag            39-23  .  . 
M177B              lc-2... 

/" 
.Do 

4 

1 

\    Tb 
Ag,  3  AgTb,  SYAgTb 

g 

M168B             Ji     .    . 

Do 

4 

1 

2  Ag,  2  AgTb,  SCrgAg 

9 

M169,  M171  B  3^ 

Do 

3 

3 

3  AgTb,  2  BrOAgTb, 

10 

B68  AgTb          la-1 

B  118  AgTb     ld-6 

6 

1 

BrYAg 
4  AgTb.  2  B,  SjCr5 

11 

A443  B               t  

A469  AgTb     $  

1 

AgTb 
LBr 

12 

M90  Br              ^  

M  189  AgTb    39-30.  . 

3 

BrOsAgTb,  S6,  Cr6 

13 

/M90Br              &  

Do 

6 

2 

3  AgTb,  3  B,  S5Cr6 

14 

\M114B              16-7... 
A1117B             3*1  

1357  B            BW.... 

2 

1 

AgTb,  S5 
AgTb,  B,  S4Cr6AgTb 

15 

A1566AgTb      j%     .    . 

A1050  AgTb  3*2  

4 

2 

3  AgTb,  BrAgTb,  SCr 

16 

Do     

AA15AgTb    sV  

2 

1 

AgTb,  S4 
AgTb,  B,  SCrAgTb 

17 

A529  BrAgTb    3*3  

Do  

5 

2 

3  AgTb,  B,  BrAgTh, 

18 

AA202  AgTb     405-8  .  . 

.  .    .Do  

2 

2 

SCrAgTb,  BrCrAg 
Tb 
2  AgTb,  2  SCrAgTb 

19 

M177B              lc-2.  .  . 

AA235  AgTb  406-7  .  . 

4 

1 

AgTb,  2  B,  BrAgTb, 

20 

M  102  AgLb       66-1... 

M2B               &. 

4 

1 

LBr-Crs 
2  Ag,  2  B,  SjCr&Ag 

21 

3392  AgLb         Misc  .  . 

A1539  B          -fa  

1 

SCrAg 

22 

3392,  3444  Ag    Misc  .  . 

Do             ... 

3 

1 

2  Ag,  B,  SCrAg 

23 

3392  Ag              Misc  .  . 

B5  AgTb         ld-16 

3 

1 

3  Ag,  S4Y4Ag 

24 

20a  Ag                Misc  .  . 

A1474  AgTb  A  

3 

1 

3  Ag,  SCrAg 

25 

A1310Ag           jV  

A1449  AgTb  s\  

2 

1 

AgTb,  B,  Cr 

26 

M203  AgTb       2-19  .  .  . 

AA284  AgTb  39-18  .  . 

4 

1 

3  AgTb,  B,  S 

27 

M82  Ag              9-7  

A1161  AgTb  sV  

1 

1 

AgTb,  SCrAgTb 

28 

AA171  R           3*5  

Do  

2 

1 

AgTb,  R,  Cr 

29 

M183B             ^  

AA299  AgTb  40-6  .  .  . 

3 

1 

3  AgTb,  SCrAgTb 

30 

20  B                    Misc  .  . 

A412R(Br)     &.    .    . 

3 

1 

2  AgTb,  B,  SCrAgTb 

31 

M7B                 &  

M133Ag         8-4  

4 

? 

2  Ag,  2  B,  SCrAg.  S6 

32 

A1420B             h- 

A811  Br          sV       •  • 

1 

1 

Br,  LBr 

33 

A385  B              jf  

12845  B           4-toe... 

4 

1 

4B,  S 

Total  

109 

H7 

1Ezcess  of  dilutes  expected  because  the  presence  of  at  least  one  dilute  young  is  used  aa  a 
criterion  for  admission  to  the  table. 


TABLES. 


147 


TABLE  101. 

Cross  40. — All  coatings  of  intense  with  dilute  which  have  given  dilute  or  albino  young, 
except  those  of  crosses  28,  29,  32  and  36. 

Expectation:  CCd  X  CdCd  =  CCd  +  CdCd  (1  Int :  1  Dil),  1. 

CCa  X  CdCd  =  CCd  +  CdCa  (Int :  1  Dil),  2-5  (5?). 
CCd  X  CdCa  =  CCd  +  CCa  +  CdCd+CdCa  (1  Int :  1  Dil),  6-19  (9, 10, 12, 
14,  15,  16,  17?). 


No 

9  Int  (or  Dil)  . 

cfDil  (or  Int). 

Int 

Dil 

RE 

W 

Remarks. 

1 

40a. 
B139  Ag                  39-23  .  . 

M328Bj-Y4             42-17. 

?, 

3 

2  AgTb,  3  SjYt 

2 

AA606  SjY.AgTb   40o-8  .  . 

AA573  Br  AgTb       40o-7  . 

1 

1 

Ag 
AgTb,  StCr6Ag 

3 

4  9  9  B                  Misc.  .  . 

AA241  SYAgTb      40o-6. 

5 

3 

Tb 
AgTb.  4  B,  S« 

4 

169  B                        4-toe... 

A656Br-Y               |  

1 

3 

CrjAgTb.  Sr- 
Cr«,  LBr 
B,  3S-Cr 

5 

AA497  SYAgTb      39-7.  .  . 

AA284AgTb            39-18. 

?, 

1 

AgTb,  R,  LBr 

6 

AA206  AgTb           39-2  .  .  . 

AA177  S«Cr«AgTb  41-4.  . 

3 

4 

3  AgTb,  SYAg 

7 

AA213AgTb           39-15.. 

AA253  S8Cr6AgTb  406-8. 

4 

5 

Tb,  2  S,Y,Ag 
Tb,  S,CrBAg 
Tb 
3  AgTb,  BrAg 

g 

AA217  AgTb          406-8  .  . 

Do  

7 

4 

Tb,  SjYjAgTb, 
BrYsAgTb,  Ss 
CrsAgTb.  S6 
CrjAgTb,  Br 
Cr^AgTb 
7  AgTb  SjYtAg 

g 

AA613AgTb          40o-7.. 

Do 

3 

Tb,2S3Y^g 
Tb,  SCrAgTb 
S^YaAgTb  SsCrj 

10 
11 
12 

3o  AgLb                   Misc.  .  . 
M261Sep4               41-2... 
M282  Ag                  15-12  .  . 

M34  Sepr-Crt          16e-l  . 
AA299AgTb            40o-6. 
M  1  16  Seps-Y4          42-1  1  . 

3 

2 
1 
1 

AgTb,  S4Crs 
AgTb 
2Sr-Cr« 
8, 
2  AgLb,  B,  S«- 

13 

30  Br                        Misc.  .  . 

M34  Sep«-Crj           16c-l  . 

1 

? 

Cr, 
R,  B2,  S» 

14 

M99  B                      42-13?  . 

Do                     .... 

?, 

1 

2  B,  S«-Cre 

15 

M101B,  M99B      42-13?. 

Do  

3 

1 

B,  2  R,  87 

16 

M99  B                      42-13?  . 

A674  Sep6                  J 

1 

Sr-Cr? 

17 

M155  B                   ^ 

Do    . 

3 

2  S«,  S7 

18 
19 

M82Ag                    9-7  

SA13B                    28-3... 
Total 

M116Sep5-Y4         42-11. 
M306S7-Cr7             42-15. 

2 

S6 

3 

2 

441 

2  AgTb,  8Y,Ag 
Tb,  BrY»Ag 
Tb,  SCr«AgTb 
Ss-Crj,  Sr-Crr 

'Excess  of  dilutes  expected. 


148 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  101 — Continued. 
Cross  40 — Continued. 


No. 

9Int  (or  Dil). 

d*Dil  (or  Int). 

Int 

Dil 

RE 

W 

Remarks. 

1 
2 

406.1 
A1659  B                   *&« 
A  1523  AgTb            ife    •    •  • 

AA253  S5CrsAgTb  406-8. 
AA199  SCrAgTb     39-15 

g 

2 
1 

2  SCrAgTb 
2  AgTb,  SCrAg 

3 

B132AgTb              ld-3... 

M293  Y4                   42-14  . 

1 

1 

Tb 
AgTb,  SeCr6Ag 

4 

5 

M442  BrCrsAgTb   39-12  .  . 
M44Cr6                   42-12.. 

AA573BrAgTb       40a-7. 
AA197AgTb           2-10.. 

2 

1 
1 

Tb 
BrCr6AgTb 
2  AgTb,  SCrAg 

6 

7 
8 

M181  BrCr6AgTb  41-6.  .  . 

AA203  BrCrAgTb  39-17.  . 
A1273SCrAgTb     3"$  

AA573  BrAgTb       40o-7  . 

AA16  AgTb             g>5  .  .  .  . 
Do  

8 

2 
8 

2 

2 

3 

2 

1 
3 

Tb 
3  BrAgTb,  Br 
CrBAgTb,  Br 
Cr6AgTb 
2  AgTb,  SCrAg 
Tb,  LBr 
AgTb,  2  B,  SCr 

9 
10 

AA176  AgTb           41-4  .  .  . 
AA175  AgTb           41^1  .  .  . 

AA177  S6Cr6AgTb  41-4.. 
Do  

5 

1 

1 
1 

AgTb,  SBCrB 
AgTb,  Sj-Y4 
4  AgTb,  B  SCr 
AgTb 

11 

AA671  AgTb           40o-7  .  . 

AA253  S6Cr6AgTb  406-8. 

1 

12 
13 

M46  BrCreAg           44-1  .  .  . 
S443Sep                  ArF2... 

Total  

A1170AgTb             sSf.... 
M156R                     &•••• 

2 
4 

?4 

1 

152 



1 

2 

I?2 

Ag,  BrAg 
4B,Sr-CrB 

Expectation:  CCa  X  CdCa  =  CCd  +  CCa  +  CdCa+  CaCa  (2  int  :  1  dil  :  1W). 
2Excess  of  dilutes  and  albinos  expected. 

TABLE  102. 

Cross  41  - — All  matings  of  intense  with  albino  which  have  given  dilute  young,  except  those 

given  in  crosses  18  and  34. 

Expectation:  CCd  X  CaCa  =  CCa  +  CdCa  (1  Int :  1  Dil). 


No. 

9  Int  (or  W). 

<7W  (or  Int). 

Int 

Dil 
2 

RE 

W 

Remarks. 

1 
2 
3 
4 
5 
6 

7 

Al  146  AgTb  jV  ... 
M102  AgLb  66-1  .  . 
B139Ag  39-23. 
A1227W  «V--- 
A1309W  £.... 
AA28W  &.. 

A504  W           t"s  .  .  . 

S,  S-Y 
B,  S4 
AgTb,  S3Cr6AgTb 
2  AgTb,  S6Cr6  AgTb 
BrAgTb,  B.  R,  R(Br),  Cr(Br) 
Ag,  BrAg.AgTb,  R,  SCrAgTb, 
BrCrsAgTb,  2  Cr 
B,  S-Cr 

A462W           &... 
20  W                BW  . 
A781AgTb    &... 
A1513AgTb  ^... 
...  Do    

1 
1 

2 
4 
4 

1 
13 

1 
1 
1 
1 

4 

1 

II1 

131  W            4-  toe.  . 
Total 

A412R(Br)     ^.  .  . 





Excess  of  dilutes  expected  though  not  found. 


TABLES. 


149 


TABLE  103. 

Cross  4&> — All  matings  of  dilute  with  dilute,  except  those  of  crosses  30  and  37. 
Expectation:  CdCd  X  CdCa  =  CdCd  +  CdCa  (all  Dil)  (M328,  AA242,  M394,  CdCd). 
CdCa  X  CdCa  =  CdCd  +  2  CdCa  +  CaCa  (3  Dil :  1  W). 


No. 

9  Dilute. 

d"  Dilute. 

Int 

Dil 

RE 

W 

Remarks. 

1 

B141  S4Y4Ag           39-23.. 

M328  Br-Y4             42-17  .  . 

4 

3  ^YaAgTb  84 

2 

AA242  SjYgAgTb   40o-6  .  . 

B117  S4CrsAgTb      39-14  .  . 

1 

CrjAg 
S6Cr8AgTb 

3 

AA244  Sep4             39-15  .  . 

Do  

1 

SgCrsAgTb 

4 

D44  Sep3                   16o-3  .  . 

Do  

1 

? 

S4Cr&AgTb 

5 

D43  Seps                  16a-3  .  . 

D94  S3Y*Ag              165-9  .  . 

2 

S3CrsAg  83 

5a 

D45  Sepr-Crs           16a-3  .  . 

Do  

? 

1 

S2  SsCr^Ag 

6 

D26  S5Cr&AgTb      16a-4  .  . 

D33  SsCr^AgTb       166-^  .  . 

1 

7 
8 

/D110Sep6                16c-3.. 
\D107  Sep4                166-1  .  . 
D215  Seps                16o-2.. 

JD  106  Sep4                 166-1  .  . 
Do  

5 
? 

1 

5S3 
Bi   Si 

9 

10 

M181  BrCrjAgTb  41-6.  .  . 
3520  Y4(Br)             Dil 

AA253  S8Cr6AgTb  406-8  .  . 
A674  Sep8                  \   •    •    • 

1 

6 

1 
1 

SY4AgTb 
S^YiAe  SsCrs 

11 

3417  Cr«                   Dil  .    .  . 

....  Do  

s 

9 

Ag,  BrCreAg, 
Y4(Br),2Cr« 
(Br) 
SK  YJ  Y^  Cr» 

12 

/3417  Cr6                   Dil  .... 

}  Do.  . 

4 

S-Cr,  LBr,  Y, 

13 

\3462  Cr6(Br)            Dil  .... 
O6  LBr-Cr              Misc. 

/ 
.Do 

19 

4 

1 

Cr6 

2B  S-Cr  87- 

14 

M127Cr6                 42-13.. 

Do  

1 

Cr7,Cr6(Br), 
Cr& 
Y4 

15 

M44Cr6                   42-12.. 

Do  

1 

1 

&j-C^ 

16 

M164Cr7                 44-6... 

Do  

9 

17 

M126  Cre(Br)          42-13.  . 

Do  

1 

1 

B—  Y4 

18 
19 

M164Cr7                 44-6... 
M44  CrB                   42-12  .  . 

M306  Sep7-Cr7         42-15  .  . 
Do  

2 
3 

1 

S7-Cr6,  Cr6 
Se-Cre  Cr7,  Cr« 

20 

M296  SCrAgTb      39-27  .  . 

M116Sep6-Y4         42-11.. 

3 

SY2AgTb  2S 

21 
22 

MSlOSepT-Crr        40a-16. 
M336  Sep«               40a-17  . 

M335Sep6                40a-17. 
Do  

1 
3 

1 

1 

Y3AgTb 

S6 

23 

M336  Sep6                

M34  Sepe-Crs           16c-l  .  . 

1 

S4-Ys 

24 

M394  Sep4               42-22  .  . 

Do  

3 

S4-Y4  Yj  Crj 

25 

/M336,Sep6              40o-17. 

1  Do  .  . 

4 

26 

\M394Sep4               42-22.. 
M393  Sep6               42-22 

/ 

Do  

1 

27 

D278  Cr5(Br)          386-5  .  . 
Total  

D138  Cr6(Br)           36-1  ... 

»2 

1 
60 



1 

19 

Cr6(Br) 

CdCd  X  CdCa  

10 

0 

CdCa  X  CdCa  

50 

19 

'Recorded  from  a  mixed  pen  before  the  study  of  dilution  was  begun,  probably  an  error. 

TABLE  104. 

Cross  43. — All  matings  of  dilute  with  red-eye,  except  those  of  crosses  20  and  26. 
Expectation:  CdCd  X  CrCa  =  CdCr  +  CdCa  (all  Dil)  (1-2). 

CdCa  X  CrCa  =  CdCr  +  CdCa  +  CrCa  +  CaCa  (2  Dil :  1  RE:  1W)  (3-4). 


No. 

9  Red-eye. 

cf  Dilute. 

Int 

Dil 

RE 

W 

Remarks. 

1 

241  SAg(R)        ArF2.. 

M328B2-Y4             42-17.. 

3 

3  SCrAg 

2 

271  SAg(R)        ArF2.  . 

M333Y2                   42-11.. 

4 

2  S6Y4Ag  2  S4Y4Ag 

3 

236  Sep(R)        ArF2.. 

M331  BrCr»Ag         42-10  .  . 

1 

4 

D194  Sep4<R)    26-2  .  . 

AA670  S6CrsAgTb  40a-7  .  . 

9 

1 

9 

S2CrjAgTb  SgCr6 

AgTb,  SjAgTb 
(R) 

150 


INHERITANCE    IN   GUINEA-PIGS. 


TABLE  105. 

Cross  44. — All  matings  of  dilute  with  albino,  except  those  of  crosses  16,  19,  27,  33,  and  38. 
Expectation:  CdCd  X  CaCa  =  CdCa  (all  Dil)  (1). 

CdCa  X  CaCa  -  CdCa  X  CaCa  (1  Dil :  1  W)  (2-6). 


No. 

9  Dil  (orW). 

tfW  (or  Dil). 

Int 

Dil 

RE 

W 

Remarks. 

1 
2 
3 

4 
5 
6 

3256BrYAgLb    Misc.. 
A505  Sep             ^  
3  9  9  W             Misc.  . 

S176S-O           ArF2.. 
S263SCr8Ag        ArF2.. 

A678W                  &.    . 

9 

7  SOaAg,  2  Br-Cre 
8 
S4,  SjOsAgTb,  Br 
Cr»AgTb,  2  S« 
2Sj-Y4 
S^rjAg 
S7Cr7Ag,  CrT 

A868W                  ^  

1 

B117S4Cr6AgTb   39-14.. 

11  W                       Dil.... 
Do  

5 

2 
1 

1 
3 

O7  W                   Misc.  . 

A674  Sep«                J  

?, 

TABLE  106. 

Cross  46. — Rough  A  (4-toe)  X  rough  A  (4-toe). 
Rrss  X  Rrss  =  3Rss+rrss(3A:l  Sm). 


No. 

9  Rough  A. 

d"  Rough  A. 

A 

B 

C 

D 

E 

Sm 

1 

3769  4-toe  

3609  4-toe 

1 

2 

96       4-toe  .  .  . 

Do 

2 

3 

("3769  4-toe  

>         Do 

5 

1 

4 

\3770  4-toe  
3769  4-toe  

I" 
3987  4-toe  

a 

5 

3770  4-toe  

Do  

? 

Total 

10 

3 

TABLE  107. 

Cross  Ifi. — Rough  A  (tricolor)  X  rough  A  (tricolor) ;  one  or  both  of  parents  of  each, 

rough  C  or  D. 

Rrss  X  Rrss  =  3  Rss  +  rrss  (3  A :  1  Sm)  (1-8). 
or  Rrss  X  RRss  =  Rss  (all  A)  (9-12?). 


No. 

9  Rough  A. 

c?  Rough  A. 

A 

B 

C 

D 

E 

Sm 

1 

4018            Tri  

3775    Tri  

1 

2 

3941            Tri  

3940    Tri  

3 

3 

3943            Tri  

Do  

1 

4 

/R65             54-17  
\3943            Tri  

|  Do  

7 

1 

5 

R65             54-17  

Do  

•?, 

?, 

6 

R171           47-3 

Do      . 

2 

2 

7 

R278           52-14  

R248  52-10  

1 

1 

8 

R357  Red  52-8  

Do  

1 

1 

1 

9 

R65             54-17  

R197  52-14  

2 

10 

R171           47-3  

Do  

3 

11 

R194           54-1  

.    .    .Do    

2 

12 

R196           52-14 

Do 

3 

Total  1  to  8 

17 

•  ' 

7 

Total  9  to  12  .  . 

10 

V 

TABLES. 


151 


TABLE  108. 

Cross  47. — Rough  A  X  rough  C  (tri);  all  mothers  of  tricolor  stock  except  R175—  4-toe. 
Rrss  X  RrSs  =  3  Rss  +  3  RSs  +  2rr  (3  A :  3  C :  2  Sm). 


No. 

9  Rough  A. 

d"  Rough  C. 

A 

B 

C 

D 

E 

Sm 

1 

R21     46-2.... 

R52  56-1  

1 

2 

2 

R23     46-2  .... 

Do  

1 

1 

3 

R42     50-1  .... 

Do  

1 

1 

1 

4 

R21     46-2.... 

R99  56-1  

1 

2 

5 

R23     46-2  .... 

Do  

1 

1 

6 

R42     50-1.... 

Do  

3 

1 

2 

4 

7 

R175  49-1  .... 

Do  

3 

1 

Total  .  .  . 

10 

1 

5 

1 

10 

TABLE  109. 

Cross  48.— Rough  A  (Tri)  X  rough  E  (Tri). 
Rrss  X  RRSS  =  RSs  (all  C). 


No. 

9  Rough  A. 

cf  Rough  E. 

A 

B 

C 

D 

E 

Sm 

1 

R42  50-1  

4003   Tri   

2 

1 

TABLE  110. 

Cross  49- — Rough  A  (4-toe)  X  smooth  (4-toe). 
Rrss  X  rrss  =  Rrss  +  rrss  (1  A :  1  Sm). 


No. 

9  Smooth. 

cf  Rough  A. 

A 

B 

C 

D 

E 

Sm 

1 

499   4-toe  

3922  4-toe  

18 

13 

2 

599   4-toe 

3609  4-toe  . 

10 

1 

19 

Total  .... 

?8 

1 

3?, 

TABLE  111. 

Cross  50. — Rough  A,  B  (tri)  X  smooth  (4-toe  etc.).     Rough  A,  B  with  one  or  both  of 

parents  paitial  rough. 

Expectation  as  in  cross  49. 


No. 

9  Smooth  (or  rough  B). 

c?  Rough  A 
(or  smooth)  . 

A 

B 

C 

D 

E 

Sm 

1 

799  Sm  4-toe 

3775  A  Tri  

13 

14 

2 

R121  Sm  50-1 

Do  

3 

3 

R62  Sm     50-1 

R22  A    46-2   

3 

3 

4 

IR163  B      52-13 

99  Sm    4-toe  

3 

Total 

19 

90 

'R163  may  be  RR. 


152 


INHERITANCE    IN    GUINEA-PIGS. 


TABLE  112. 

Cross  51 . — Rough  A  X  smooth  (tri) ;  smooth  with  one  or  both  parents  partial  rough. 
Rrss  X  rrSS  =  RrSs  +  rrSs  (1  C :  1  Sm). 
Rrss  X  rrSs  =  Rrss+  RrSs  +  2rr(lA:lC:2 Sm). 
Rrss  X  rrss   =  Rrss  +  rrss  (1  A  :  1  Sm). 


No. 

9  Smooth. 

cf  Rough  A. 

A 

B 

C 

D 

E 

Sm 

1 

R13                52-1  

R22  46-2  

1 

3 

4 

2 

R123              54-3  

R76  4-toe  

2 

4 

3 

R124              54-3  

Do  

1 

2 

4 

R133              47-2   

Do  

2 

5 

R124,  R133  

Do  

2 

8 

6 

R142              54-3  

Do  

1 

1 

Total  

6 

3 

3 

19 

TABLE  113. 

Cross  52.— Rough1  C,  D  (tri)  X  rough  C  (tri). 
RrSa  X  RrSs  =  3  Rss  +  6  RSs  +  3  RSS  +  4rr(3A:6C:3E:4  Sm). 


No. 

9  Rough  C,  D. 

d"Rough  C. 

A 

B 

C 

C 

E 

Sm 

Remarks. 

1 

3013             Tri  

3780  Tri  

1 

3 

1 

1 

? 

2 

3246             Tri  

Do  

1 

? 

3 

Rll              52-1  

Do  

1 

2 

3 

4 

R54              52-1    .... 

.  .    .Do  

1 

1 

5 

3245             Tri 

4019  Tri    .    ... 

2 

1 

6 

3939             Tri 

R58   52-5     . 

4 

1 

1 

Red-A 

7 

3809             Tri  

Do  

2 

1 

Red-E,  Red-Sm 

8 

3246             Tri  

Do  

?, 

1 

1 

Red-A 

g 

3724  D         Tri  

Do  

1 

1 

10 

3724  3246  Tri  

Do  

1 

4 

1 

11 

R51              56-1  

R56   56-1  .    ... 

? 

1 

2 

2 

1 

s 

12 
13 

R57              56-1  
R51  R57    56-1 

Do  
.  .     Do    

1 

1 

1 

2 

14 

R98              56-1 

Do        .      . 

5 

? 

3 

1 

15 

R103            56-1  

Do  

1 

1 

5 

1 

1 

Red-C 

Total  

18 

A 

19 

7 

}?, 

17 

1AII  rough  C  except  3724. 

TABLE  114. 
Cross  53.— Rough  C,  D  (tri)  X  rough  E  (tri). 

RrSs  X  RRSS=  RSs  +  RSS  (1  C:  1  E). 
or  RRSsX  RrSS  =  RSs  +  RSS  (1  C :  1  E). 
or  RrSa  X  RrSS  =  3  RSs  +  3  RSS  +  2  rr  (3  C  :3  E  :  2  Sm). 


No. 

9  Rough  C,  D. 

d"  Rough  E. 

A 

B 

C 

D 

E 

Sm 

1 

R6  D      54-15  .... 

4003            Tri  

1 

?, 

2 

R88  C     52-1    .  .    . 

R200  Red  52-7  

2 

3 

R286  C  52-6  . 

R280           52-14  .... 

3 

4 

R222  C  52-12  .... 

Do  

1 

?, 

1 

Total 

4 

1 

6 

1 

TABLES. 


153 


TABLE  115. 

Cross  54. — Rough  C,  D  (tri)  X  smooth  (4-toe,  etc.). 
RrSs  X  rrss  -  Rrss  +  RrSs  +  2rr(lA:lC:2  Sm). 


No. 

9  Smooth  (or  rough  C,D). 

cf  Rough  C,D 
(or  smooth). 

A 

B 

C 

D 

E 

Sm 

1 

399  Sm                4-toe  . 

3780  C     Tri 

1 

1 

8 

2 

R62  Sm                   60-1  

Do  

? 

2 

3 

599  Sm               4-toe 

R12  C      52-1 

4 

12 

17 

4 

399  Sm               4-toe  

R26  D      54-15  

8 

3 

fi 

14 

5 

499  Sm                4-toe  

R52  C      56-1  

2 

2 

6 

6 

599  Sm                4-toe  

R102  C    56-1  

4 

5 

3 

9 

7 

B31  Sm                    ld-9  

R105  C    48-1  

2 

g 

M253Sm                la-10  

R106  C    48-1  

2 

9 

M255Sm                la-10  

Do  

1 

10 

M380  Sm                ^j  

Do  

1 

11 

131,  M253,  M255  Sm  

Do  

1 

3 

12 

M384  Sep-Sm        1&-9  

R99  C      56-1   . 

2 

2 

13 

R62  Sm                  50-1  

R112C    52-11  

3 

14 

65  Sm                     4-toe  

.    .  .  Do  

1 

1 

1 

15 

3246  C                     Tri  

2967  Sm  BB 

5 

1 

2 

3 

16 

3809  C                     Tri  

Do  ... 

1 

3 

17 

3724  D                     Tri  

.  .  .    .Do  .      . 

3 

1 

1 

8 

Total  

34 

29 

13 

1 

79 

TABLE  116. 

Cross  55.— Rough  E  (tri)  X  rough  E  (tri). 
RrSS  X  RrSS  =  3  RSS  +  rrSS  (3  E :  1  Sm). 


No. 

9  Rough  E. 

cf  Rough  E. 

A 

B 

C 

D 

E 

Sm 

1 

R221         52-12 

R140  52-3 

? 

3 

2 

*R201  Sm  52-7 

Do 

?, 

Total  

4 

3 

^ee  note,  cross  57. 

TABLE  117. 
Cross  56.— Rough  E  (tri)  X  smooth  (4-toe). 

RRSS  X  rres  =  RrSs  (all  C)  1. 

RrSS    X  rrss  =  RrSs  +  rrSs  (1  C :  1  Sm)  2-5. 


No. 

9  Smooth 
(or  rough  E). 

c?  Rough  E  (or 
smooth). 

A 

B 

C 

D 

E 

Sm 

1 

399  Sm    4-toe 

4003  E       Tri  

11 

2 

1  9  Sm        4-toe 

R140  E      52-3  

1 

3 

3 

B31  Sm      la-1 

....  Do  

?, 

4 

JR201  Sm    52-7 

13  W-Sm  4-toe  .... 

1 

1 

5 

R221  E      52-12 

Do  

?, 

Total  (1) 

11 

Total  (2-5) 

2 

8 

*See  note,  cross  57. 


154 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  118. 

Cross  57. — Smooth  (tri)  X  smooth  (4-toe,  etc.);  both  parents  of  tricolor  smooths  were  partial 

roughs  (cross  52). 
rr  X  rr  =  rr  (all  Sm). 

If,  however,  RSS,  normally  rough  E,  is  ever  Sm: 
RrSS  X  rrss  =  RrSs  +  rrSs  (1  C :  1  Sm). 


No. 

?  Smooth. 

c?  Smooth. 

A 

B 

C 

D 

E 

Sm 

1 

699  

R131  52-4  

14 

2 

R139           52-3  

99        4-toe  

2 

3 

R13             52-1  

Do  

8 

4 

R164           52-13  

Do  

? 

5 

R199  Red  52-7  

13  W  4-toe  

3 

6 

R249           52-10  

Do  

3 

7 

R263           52-11.  .  .      . 

Do  

2 

8 

XR201           62-7  

Do  

1 

1 

*R201  was  called  rough  E?  at  birth  with  the  note  that  there  seemed  to  be  a 
trace  of  roughness  on  one  hind  toe.  No  roughness  was  apparent  when  adult  and 
she  was  called  Sm,  but  nevertheless  was  tested  by  mating  with  a  4-toe  smooth. 
The  result  shows  that  she  was,  genetically  at  least,  like  a  rough  E. 

TABLE  119. 
Cross  68. — Rough  B,  C  (Lima)  X  rough  B  (Lima). 


No. 

9  Rough  B. 

c?  Rough  B. 

A 

B 

C 

D 

E 

Sm 

1 

TV7                             Tnnnfl.  , 

L5      Lima  .  .  . 

9, 

? 

1 

?, 

L97                     60-6  

L26    58-1  

1 

8 

L140                   60-7  

Do  

1 

1 

4 

/L97                     60-6  

>L98    60-6 

? 

9 

? 

5 

\L81  Red             59-3  
L99  Rough  C     61-1  .  .    . 

Do  

1 

1 

6 

LSI,  L97,  L99     (above)  . 

Do  

1 

1 

2 

4 

Total  

8 

7 

?, 

1 



7 

TABLE  120. 
Cross  59. — Rough  A  (Lima)  X  smooth  (Lima). 


No. 

9  Smooth  (or  rough  A). 

d"  Rough  A  (or  smooth). 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

L13  Sm                62-2  .  . 

L9  A                   58-1  .  . 

?, 

1 

?, 

L14Sm                60-1   . 

Do  

7 

1 

?, 

3 

L24  Sm                 60-2 

.Do  

9: 

1 

3 

ft 

Red-B 

4 

L25  Sm                 58-1 

.Do  

4 

1 

3 

2  Red-A,  2 

5 

L37  Sm                62-3 

.  .    .  .  Do       

1 

Red-Sm 

6 

L57  Sm                59-3 

.Do           

1 

? 

3 

Red-A 

7 

L24,  L57  Sm       (above) 

Do           

1 

?, 

1 

Red-B 

8 

L22  A                   60-2 

LI  Sm                  Lima 

4 

1 

6 

2  Sep(p)-Sm 

ft 

L62  A                  59-3 

Do 

1 

?  • 

10 

L100  Sep(p)-A    61-1 

L82  Sep(p)-Sm  59-8 

?, 

2  Sep(p)-A 

Total  .... 

94 

8 

3 





?3" 

TABLES. 


155 


TABLE  121. 
Cross  60. — Rough  B  (Lima)  X  smooth  (Lima) . 


No. 

9  Smooth. 

cf  Rough  B. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

L4                 Lima  . 

L5        Lima  . 

3 

?! 

? 

Red-A.  2  Red-B,  Red-Sm 

2 

L6  Sep(p)     Lima  . 

Do  

?, 

1 

3 

L34               62-2   . 

L26      68-1 

?, 

? 

4 

L37               62-3 

Do  

1 

5 

L43               62-1  .  . 

Do  

1 

3 

fl 

L34,  L43     (above) 

Do  

?, 

8 

7 

L41,  L43      62-1  .  . 

Do  

?, 

3 

8 

L132             60-3  .  . 

Do  

1 

1 

9 

L75               60-4.. 

Do  

1 

1 

10 

f  L14               60-1  .  . 
|  L24               60-2 

[L131    60-3 

1 

8 

Red-Sm 

[L25               58-1  .  . 
Total  

8 

9 







30 

TABLE  122. 
Cross  61. — Rough  C  (Lima)  X  smooth  (Lima). 


No. 

9  Rough  C. 

d"  Smooth. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

L56    59-3  

LI    Lima  .... 

?! 

1 

1 

? 

Sep(p)-A 

TABLE  123 

Cross  62. — Smooth  (Lima)  X  smooth  (Lima). 
Offspring  all  smooth. 


No. 

9  Smooth. 

c^Smooth. 

B 

Red 

Sep(p) 

Red(p) 

1 
2 
3 

4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 

L3  B                Lima  .  . 
L2  Red           Lima  .  . 

LI  B                Lima  .  . 
Do  

4 
3 
4 
1 

2 
3 
3 
3 
1 
8 
1 
7 
4 
4 
6 

4 

2 

1 

1 
1 

1 

3 

1 
1 

2 

2 
4 

L8  Red           Lima  .  . 

Do  

L2,  L8  Red     Lima  .  . 

Do  

L12  Red          62-2... 
Do  

Lll  Red         62-2.  .  . 

L40  Red          62-1  .  .  . 

L35  Red          62-3  .  .  . 

Do  

L17  Red          62-3  .  .  . 

Do  

L8  Red           Lima  .  . 

Do  

L8,  L17  Red    (above) 
L64  Red          62-13.. 
L6  Sep(p)       Lima  .  . 
L19  Sep(p)     62-3  .  .  . 

Do  

L59  Red          62-3  . 

LI  B               Lima  .  . 
Do  

1 

2 

L6  Sep(p)        Lima  .  . 
L19  Sep(p)     62-3.    . 

L18Sep(p)     62-3... 
.  .    .  .  Do  

Do  

L82  Sep(p)     59-8... 
L59  (Red)       62-3... 
Do  

2 

3 

L58Red(p)     62-3... 
L121  Red(p)  62-11.  . 

Do  

L149Red(p)  62-11.  . 
Do  

L120  Red(p)  62-11.  . 

156 


INHERITANCE    IN    GUINEA-PIGS. 


TABLE  124. 
Cross  63. — Rough  A,  B  (Lima)  X  smooth  (4-toe,  etc.). 


No. 

9  Rough  A  (or  smooth)  . 

c?  Smooth 
(or  rough  A). 

A 

B 

C 

D 

E 

Sm 

1 

L107  A            59-9  .... 

13W-Sm   4-toe  

9, 

1 

2 

L108  A            59-7  

Do  

1 

3 

L110B           59-7  

Do  

1 

T 

4 

D180  W-Sm  18c-14.  . 

L98  B        60-6  

?, 

1 

5 

D236  W-Sm  17d-7.  .  . 

Do  

?, 

1 

Total  .  .  . 

4 

4 







4 

TABLE  125. 

Cross  64. — Rough  C  (low  grade  due  to  C.  rufescens)  X  smooth  (4-toe,  etc.). 
RrSs  X  rrss  =  Rrse  +  RrSs  +  2rr(lA:lC:2  Sm). 


No. 

9  Rough  C. 

cf  Smooth. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

A606  Ag       \  .  .    .  . 

166     .4-toe... 

2 

2B-C 

2 

A1687           64-1    . 

99        4-toe  .  .  . 

1 

B-Sm 

3 

A1688  Ag     65-1 

AA83  fa 

3 

4 

BrAgTb-A,  2  AgTb-A,  4 

Total  .  . 

s 



f, 





5 

AgSm 

TABLE  126. 
Cross  65. — Smooth  (some  C.  rufescens  blood)  X  rough  A. 

rrSs  X  Rrss  =  Rrss  +  RrSs  +  2rr  (1  A :  1  C :  2  Sm). 
rrss  X  Rrss  =  Rrss  X  rrss  (1  A :  1  Sm). 


No. 

9  Smooth. 

cf  Rough  A. 

A 

B 

C 

D 

E 

Sm 

1 

A702  AgTb     fa  

2597  Ag  stock 

1 

1 

2 

A605                i 

..      .Do. 

1 

1 

3 

A642                j  

Do  

?, 

4 

A842                1  

Do  

2 

3 

fi 

A913AgTb     fa  

Do  

2 

6 

699  AgTb  Ti«-¥iif. 

Do  

7 

}?, 

7 

B238                la-5  .... 

R88                    52-1 

9 

4 

8 

fB240                la-5.... 

\  Do  .  . 

2 

5 

\K61,  K62        78-6.... 

/ 

TABLES. 


157 


TABLE  127. 

Cross  66. — Rough  A  X  smooth;  both  parents  with  a  little  C.  rufescens  blood. 
Rrss  X  rrss  =  Rrss  +  rrss  (1  A :  1  Sm). 


No. 

9  Rough  A. 

cfSmooth. 

A 

B 

C 

D 

E 

3m 

Remarks. 

1 

A1690Ag  65-5.. 

AA83  B-Sm   ^j  .  .  . 

4 

1 

4 

3  AgTb-A,  Red-A,  Ag 

?, 

Do  

M91  Ag-Sm  8-4.. 

? 

4 

Tb-B,  AgLb-Sm,  Ag 
Tb-Sm,  2  Red-Sin 
2  AgLb-A,  2  AgLb-Sm, 

a 

A1691  Ag  65-5.. 

AA83  B-Sm   ^  •  •  • 

8 

4 

2  AgTb-Sm 
4  AgLb-A,  4  B-A,  2  Ag 

Total  

14 

1 





— 

1? 

Lb-Sm,  2  B-Sm 

TABLE  128. 
Cross  67. — Rough  A  (4-toe,  tri)  X  smooth  (pure  lea). 

Rrss  X  rrSS  =  RrSs  +  rrSs  (1  C :  1  Sm). 
Young  all  light-bellied  agouti. 


No. 

9  Rough  A. 

d*  Smooth. 

A 

B 

C 

D 

E 

Sm 

1 

2 
3 
4 

/R215   49-1  .... 
\R252    49-2.... 
R236   50-3 

J724  SAg(R)    lea  .... 

3 

Do  

2 

1 
1 
2 

4 

R205   46-4 

.    .  .  Do  

R213    49-1 

.  .  Do  

Total 





6 





TABLE  129. 
Cross  68. — Rough  A  X  smooth  (pure  C.  cutleri). 

Rrss  X  rrSS  =  RrSs  +  rrSs  (1  C :  1  Sm). 
Young  all  light-bellied  agouti. 


No. 

9  Rough  A. 

cfSmooth. 

A 

B 

C 

D 

E 

Sm 

1 

3986              4-toe 

C128  Ag   .... 

1 

?, 

2 

3988              4-toe... 

Do  

2 

1 

3 

3986,3988    4-toe... 

Do  

2 

3 

4 

A1691  Ag     65-5  .  .  . 

Do  

1 

2 

3 

5 

AA567Ag    66-3... 

Do  

1 

3 

6 

/AA568          66-3... 
\R80               54-15.. 

J....DO  

... 

3 

Total 

3 

6 

15 

158 


INHERITANCE    IN    GUINEA-PIGS. 


TABLE  130. 

Cross  69. — Rough  C  (tricolor)  X  smooth  (pure  C.  cutleri). 
RrSs  X  rrSS  =  RrSs  +  RrSS  +2rr(lC:lE:2  Sm). 
Young  all  light-bellied  agouti. 


No. 

?  Black  rough  C.  D. 

cf  Smooth. 

A 

B 

C 

D 

E 

Sm 

1 

3245               Tri  

C128Ag  

? 

2 

R54                52-1  .  .  . 

Do  

1 

1 

1 

3 

R152              54-4  .  .  . 

Do  

1 

? 

4 

3245,  R110    

Do  

?, 

1 

5 

R110              51-1... 

Do  

?, 

1 

6 

R170              47-3  .  .  . 

Do  

1 

a 

7 

Rll                52-1... 

Do  

1 

8 

RIGID         52-5... 

Do  

3 

9 

R154  D         54-4  .  . 

Do  .  .    .    . 

a 

Total  ...    . 





1 

1 

q 

T> 

TABLE  131. 
Cross  70. — Rough  A  (guinea-pig)  X  rough  C,  D  (J,  J  cutleri). 


Rrss  X  RrSs  =  Rss  +  RSs  +  2rr  (3  A :  3  C :  2  Sm). 
All  |  cutleri  Rough  C,  D,  except  K58,  J  blood. 
R116  and  R137  may  be  RRsa. 


No. 

9RoughA(orC,D). 

d"  Rough  D(orA). 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

R116B-A    46-4.. 

K54  Ag-D    68-1  .  . 

a 

1 

Ag-A,  B-A,  Ag-C 

2 

R117B-A    46-4.. 

Do  

1 

1 

B-D,  B-Sm 

3 

R137  B-A    47-1  .  . 

Do  

?: 

2B-C 

4 

AA608  B-A  66-3  .  . 

Do  

3 

1 

Ag-A,  2  B-A,  Ag-E 

5 

K12  Ag-D  68-3  .  . 

R31  B-A       45-3.. 

a 

1 

2  B-C,  B-Sm 

6 

K14  Ag-D   68-3.  . 

Do  

a 

2  Ag-B 

7 

Do  

3609  B-A      4-toe  . 

1 

i 

1 

B-A,  Ag-B,  Ag-E 

8 

Do  

R76  B-A       45-4   . 

1 

1 

B-A,  B-D 

9 

K12Ag-D   68-3    . 

Do  

1 

? 

1 

Ag-A,  2  Ag-C,  B-Sm 

10 

K58B-C      70-5. 

Do  

i 

1 

B-C,  B-Sm 

Total  .  .  . 

8 

3 

8 

9 

a 

4 

TABLE  132. 
Cross  71. — Rough  A  (guinea-pig)  X  smooth  (5,  J  cutleri). 

Rrss  X  rrSs  =  Rrss  +  RrSs  +  2rr  (1  A :  1  C :  2  Sm). 
All  i  cutleri  except  K79,  \  cutleri. 


No. 

9  Smooth. 

cf  Rough  A. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

K7Ag      77-1    . 

R31  B    45-3. 

3 

? 

1 

7 

Ag-A,  2  B-A,  2  B-B,  B-C,  6 

2 

K15Ag    68-3.. 

Do  

3 

? 

q 

Ag-Sm,  B-Sm 
Ag-A,  2  B-A,  Ag-C,  B-C,  3 

3 

K55  Ag    68-1  . 

Do  

? 

1 

Ag-Sm,  6  B-Sm 
2  Ag-C,  B-Sm 

4 

K7,  K55  (above) 

Do  

? 

3 

2  Ag-A,  2  Ag-Sm,  B-Sm 

5 

K68  Ag    77-1  . 

Do  

1 

1 

? 

1 

B-A,  B-B,  Ag-D,  2  B-C 

6 

K116  Ag  68-6 

Do  

1 

B-Sm 

7 

K81  Ag    69-1  . 

3609  B  4-toe  . 

1 

1 

Ag-C,  Ag-Sm 

8 

K79  B       78-1  . 

3922  B  4-toe  . 

1 

1 

B-A,  B-C 

Total  

10 

3 

q 

1 



?? 

\ 

TABLES. 


159 


TABLE  133. 
Cross  72. — Smooth  (guinea-pig)  X  rough  C,  D  ($,  J  cutleri). 

rres  X  RrSs  =  Rrss  +  RrSs  +  2rr  (1  A :  1  C  :  2  Sm). 
K71a,  K92  may  be  RR. 


No. 

9  Rough  C,  D(orSm). 

cf  Smooth 
(or  rough  C,  D). 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

K12  Ag-D           68-3  .  .  . 

OOCr(Br)Sm  Dil  

1 

2 

Ag-A,  2  B-D 

?, 

K14  Ag-D            68-3  .  .  . 

Do  

3 

6 

2  Ag-A,  B-A,  3 

3 

fK12  Ag-D           68-3 

}  Do  .  . 

1 

3 

Ag-Sm,  3  B- 
Sm 
fB-C,  2  Ag-Sm, 

4 

\A71a  Ag-C          70-1  .  .  . 
K92  Ag-C             70-9  .  .  . 

/ 
Do  

1 

7, 

\    B-Sm 
Ag-A,  2  Ag-C 

5 

K157Ag-C          72-12.. 

13Cr(Br)SmDil...  . 

1 

1 

Ag—  A,  Sep—  Sm 

6 

K147  AgTb-D     72-13  .  . 

Do  

3 

2  B-Sm,Sep-Sm 

7 

K142  B-D            72-1  .  .  . 

OOCr(Br)SmDil...  . 

1 

1 

1 

Red-A,  W-D, 

8 

D40Cr(Br)Sm    36-1... 

K60  Ag-C       71-2  .  . 

1 

1 

B-Sm 
B-A,  Ag-Sm 

9 

R173  B-Sm         49-1  .  .  . 

Do  

1 

1 

Ag—  A,  Ag—  Sm 

in 

20  B-Sm               4-toe  .  . 

K54  Ag-D       68-1  .  . 

?, 

1 

2 

Ag-A,  B-A,  Ag- 

11 

AA533Ag-Sm     66-2... 

K56B-C         70-5.. 

1 

C,  2  B-Sm 
Ag-Sm 

i?i 

AA586  Ag-Sm     106-10  . 

Do  

1 

1 

Ag-C,  B-D 

13 

fM382  AgTb-Sm  16-9.  .  . 

Do  

1 

1 

2 

1 

f  B-A,  3  AgTb- 

14 

\B239  AgTb-Sm  la-5  .  .  . 
B239  AgTb-Sm  la-5  .  .  . 

Do  

1 

\  C+D,B-Sm 
B-Sm 

Total  

1? 



6 

6 



?1 

TABLE  134. 

Cross  73.— Smooth  (4-toe)  X  rough  A,  B  (J  cutleri). 
rrss  X  Rrss  =  Rrss  +  rrss  (1  A :  1  Sm). 


No. 

9  Rough  A,  B. 

c?  Smooth. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

K95  B-B       71-1  

99  B     4-toe 

1 

B-Sm 

2 

fKlOlB-A     70-8  

J13W   4-toe... 

?, 

1 

2  B-A,  B-Sm 

\K106  B-A      71-2  
Total  

J 

? 



— 





? 

TABLE  135. 
Cross  74-  —  Smooth  (£,  \  cutleri)  X  rough  A 

rrSs  X  Rrss  =  Rrss  +  RrSs  +  2rr  (1  A  :  1  C  :  2  Sm). 
rrss  X  Rrss  =  Rrss  -j-  rrss  (1  A  :  1  Sm). 


cutleri). 


No. 

9  Smooth. 

cf  Rough  A. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

K68  Ag          77-1 

K59  B   71-2  .  . 

1 

B-C 

2 

K42  B             78-2  

Do  

1 

B-Sm 

Total  





1 





1 

160 


INHERITANCE   IN   GUINEA-PIGS. 


TABLE  136. 

Cross  75. — Rough  A,  B  (\  cutleri)  X  rough  A  (£  cutleri). 
Rrss  X  Rrss  =  3Rss  +  rrss(3A:l  Sm). 


No. 

9  Rough  A,  B. 

cT  Rough  A. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

K50  Ag-B      70-6  

K59B   71-2 

1 

B-A 

?, 

K53  B            71-1  

Do  

? 

2B-A 

Total  

s 











TABLE  137. 

Cross  76.— Rough  C  (f  cutleri)  X  rough  C  (i  cutleri). 
RSs  X  RSs  =  Has  +  2  RSs  +  RSS  (1  A :  2  C  :  1  E  :  ?  Sm  ?). 


No. 

9  Rough  C. 

c?  Rough  C. 

A 

B 

C 

D 

E 

Sm 

Remarks. 

1 

K114B     74-1  

K93  Ag    70-9  .  . 

1 

3 

1 

fAg-C,   Ag-D,    2   B-D, 

I    Ag-E 

TABLE  138. 

Cross  77. — Black  (BB)  X  agouti  (pure  cutleri). 
Parents  and  offspring  all  smooth. 


No. 

9  Black. 

c?  Agouti. 

AgLb 

Black 

W 

1 

2  B  9  9     BB  

C128Ag    pureC  

6 

TABLE  139. 
Cross  78.— Black  (BW)  X  agouti^,  \,  J  cutleri). 

Expectation :  1  Ag :  1  black :  some  white. 
Parents  and  offspring  all  smooth. 


No. 

9  Black  (or  agouti)  . 

%  cf  Agouti  (or  black). 

AgLb 

Black 

W 

1 

6B  9  9          BW 

C67  Ag            (i)    -  .  .  . 

12 

12 

6 

?: 

2B  9  9          BW  

K4Ag(J)       78-1  

6 

9 

3 
4 

3B  9  9          BW  
K20  Ag  (})     78-1  

K24  Ag  (i)     78-1  .... 
39  B  BW  

9 
3 

5 

fi 

K22  Ag  (})     78-1  

Do  

1 

1 

6 

K29  Ag  (i)     78-1  

Do  

3 

3 

7 

K103Ag(i)   78-4... 

Do  

2 

8 

K66Ag(i)     78-2.    . 

Do  

4 

9 

K109Ag(i)   78-6.    . 

Do  

1 

1 

in 

3B  9  9          BW..   . 

K104Ag(J)   78-4  

5 

3 

Total  

35 

41 

10 

PART  III 

FURTHER  STUDIES  OF  PIEBALD  RATS  AND  SELECTION, 
WITH  OBSERVATIONS  ON  GAMETIC  COUPLING 


BY  W.  E.  CASTLE 


THE  PROGENY  OF  HOODED  RATS  TWICE  CROSSED 
WITH  WILD  RATS. 

In  1914  Castle  and  Phillips  published  a  report  on  breeding  experi- 
ments with  hooded  rats,  in  which  it  was  shown  that  the  hooded  color 
pattern — itself  a  Mendelian  recessive  character  in  crosses  with  the 
entirely  colored  (or  "self")  coat  of  wild  rats — is  subject  to  quantitative 
variation,  and  that  different  quantitative  conditions  of  the  hooded 
pattern  are  heritable.  (Compare  fig.  36,  plate  7.)  It  was  also  shown 
that  by  repeated  selection  of  the  more  extreme  variations  in  the  hooded 
pattern  (either  plus  or  minus)  it  is  possible  gradually  to  modify  the  racial 
mean,  mode,  and  range  as  regards  these  fluctuations,  without  eliminat- 
ing further  fluctuation  or  greatly  reducing  its  amount.  We  concluded 
that  the  unit  character,  hooded  color  pattern,  is  a  quantitatively  vary- 
ing one,  but  were  at  that  time  unable  to  decide  whether  the  observed 
variability  was  due  simply  and  exclusively  to  variation  in  a  single 
Mendelian  unit  factor  or  partly  to  independent  and  subsidiary  modify- 
ing Mendelian  factors! 

Since  publication  of  the  above  I  have  been  engaged  in  further  experi- 
ments designed  to  show  which  of  the  alternative  explanations  is  the 
correct  one,  and  these  are  now  sufficiently  advanced  to  indicate  definite 
conclusions.  Previous  experiments  had  shown  that  when  a  race  of 
hooded  rats,  whose  character  has  been  modified  by  selection  (either 
plus  or  minus),  is  crossed  with  wild  rats,  the  extracted  hooded  animals 
obtained  in  F2  as  recessives  show  regression  toward  the  mean  condition 
of  the  recessive  race  before  selection  began.  This  result  suggested 
that  the  regression  observed  might  be  due  to  removal  by  the  cross  of 
modifying  factors,  which  selection  had  accumulated  in  the  hooded  race. 
If  this  view  was  correct,  it  was  thought  that  further  crossing  of  the 
extracted  hooded  animals  with  the  same  wild  race  should  result  in 
further  regression,  and  that  if  this  further  regression  was  not  observed 
a  different  explanation  must  be  sought  for  the  regression  already  noted. 

The  entire  experiment  has  accordingly  been  repeated  from  the 
beginning,  with  the  same  result  as  regards  regression  in  the  first  F2 
generation,  but  with  no  regression  of  the  same  sort  in  a  second  F2  con- 
taining twice-extracted  hooded  animals.  So  far  from  observing  further 
regression  as  a  result  of  the  second  cross  with  wild  rats,  we  have  unmis- 
takable evidence  that  the  movement  of  the  mean,  mode,  and  range  of 
the  hooded  character  has  been  in  the  reverse  direction.  So  the  hypothe- 
sis of  modifying  factors  to  account  for  the  regression  and  for  the  pro- 
gressive changes  observed  under  selection  becomes  untenable. 

In  repeating  the  experiment  of  crossing  hooded  rats  of  our  selected 
races  with  wild  rats,  great  care  has  been  taken  to  employ  as  parents 
individuals  of  the  greatest  racial  purity  and  to  inbreed  the  offspring 

163 


164 


INHERITANCE   IN   RATS. 


brother  with  sister,  thus  precluding  the  possibility  of  introducing 
modifying  factors  from  other  sources.  In  making  the  second  set  of 
crosses,  the  extracted  individual  has,  wherever  possible,  been  crossed 
with  its  own  wild  grandparent.  In  the  few  cases  hi  which  this  was 
impossible,  wild  animals  of  the  same  stock  have  been  used.  This  stock 
consisted  of  a  colony  of  wild  rats  which  invaded  the  basement  of  the 
Bussey  Institution  apparently  from  a  nearby  stable.  Owing  to  faulty 
construction  of  the  building  they  were  able  to  breed  in  spots  inaccessible 
to  us,  and  it  took  many  months  of  continuous  and  persistent  trapping 
to  secure  their  extermination.  During  this  period  we  trapped  a  hun- 
dred or  more  of  them,  all  typical  Norway  rats,  colored  all  over,  without 
even  the  white  spot  occasionally  seen  on  the  chest  of  wild  rats.  Two 
generations  of  rats  from  this  wild  stock  have  been  reared  in  the  labora- 
tory, and  all  have  this  same  self-colored  condition. 

The  hooded  animals  used  in  the  experiments  to  be  reported  on  in 
this  connection  consisted  of  4  individuals  of  the  plus-selected  series, 
a  male  and  3  females,  as  follows: 

TABLE  140. 


Individual. 

Grade.1 

Generation. 

95513  

+4i 

10 

d"6348  

+4 

10 

96600.... 

+4i 

12 

96955.... 

+4 

12 

^ee  figure  35,  plate  7,  for  significance  of  the  grades. 

Each  of  these  animals  was  mated  with  a  single  wild  mate,  and  their 
children  were  weaned  directly  into  breeding  cages  containing  a  male 
and  two  or  three  females  (brother  and  sisters).  In  the  case  of  two 
matings,  F!  males  of  the  same  parentage  were  at  the  time  lacking  and 
males  from  a  different  cross  were  used.  The  results  of  such  matings  are 
tabulated  by  themselves  and  serve  a  useful  purpose  as  controls.  The  F! 
animals  all  closely  resembled  their  wild  parents,  but  many  of  them  had 
a  white  spot  on  the  chest.  They  ranged  from  grade  +5£  to  +6  (self). 

The  F2  animals  are  classified  in  table  141,  where  it  appears  that  73 
of  them  were  hooded  and  219  non-hooded  (i.  e.,  like  Fx),  an  exact  1 :  3 
ratio.  More  than  half  of  this  F2  generation  consists  of  the  grand- 
children of  95513,  produced  by  breeding  her  children  brother  with 
sister,  those  children  all  having  been  sired  by  the  same  wild  rat.  Her 
grandchildren  include  41  hooded  and  107  non-hooded  young.  The 
hooded  young  range  in  grade  from  +  1£  to  -f-4,  their  mean  grade  being 
+3.05,  a  considerable  regression  from  the  grade  of  the  grandmother, 
which  was  4.25. 

Hooded  rats  of  the  same  grade  and  generation  as  the  grandmother, 
when  bred  with  each  other,  produced  young  of  mean  grade  +3.84. 


HOODED   CROSSED   WITH  WILD.  165 

(See  table  10,  Castle  and  Phillips.)  The  mean  of  the  extracted 
hooded  grandchildren  in  this  case  (being  3.05)  shows  a  regression  of 
0.79  from  that  expected  for  the  uncrossed  hooded  race.  From  the 
extracted  hooded  grandchildren  of  9  5513,  produced  as  just  described 
by  a  cross  with  a  wild  male,  7  individuals,  2  males  and  5  females,  were 
selected  for  a  second  cross  with  the  wild  race.  They  ranged  in  grade 
from  +2  to  +3|.  (See  table  142.)  They  produced  several  litters  of 
young  of  the  same  character  as  the  first  F!  young,  all  being  similar  to 
wild  rats  in  appearance,  except  for  the  frequent  occurrence  of  a  white 
spot  on  the  belly.  These  second  F!  young  were  at  weaning  time  mated, 
brother  with  sister,  in  breeding-pens,  precisely  as  had  been  done  with  the 
first  FI'S.  They  produced  394  second  F2  young,  of  which  98  were  hooded 
and  296  non-hooded,  a  perfect  1 :  3  ratio.  The  hooded  young  varied 
in  grade  from  +2  to  +4;  as  shown  in  table  142,  the  data  there  being 
given  for  each  family  separately  as  well  as  for  all  combined  in  the  totals. 
One  family  was  very  like  another  as  regards  the  character  of  the  hooded 
young,  except  that  the  higher-grade  grandparents  had  grandchildren 
of  slightly  higher  grade.  Thus  the  average  of  all  the  98  hooded  young 
was  +3.47,  but  the  average  of  those  descended  from  the  3  grandparents 
of  lowest  grade  was  less  than  this,  while  the  average  of  those  descended 
from  the  3  grandparents  of  highest  grade  was  greater.  This  is  just  what 
had  been  observed  throughout  the  entire  selection  experiments.  (See 
Castle  and  Phillips.) 

If  we  weight  each  of  the  grandparents  in  table  142  in  proportion  to 
the  number  of  its  hooded  grandchildren,  then  the  mean  grade  of  all  the 
grandparents  is  +2.95.  Since  the  mean  grade  of  all  the  41  first  F2 
hooded  grandchildren,  from  which  these  7  were  chosen,  was  +3.05,  it 
will  be  seen  that  these  7  are,  so  far  as  grade  is  concerned,  fair  repre- 
sentatives of  the  41,  being  in  fact  of  slightly  lower  mean  grade.  It  is 
therefore  all  the  more  striking  that  their  grandchildren,  the  second  F2 
hooded  young  (table  142) ,  are  of  higher  grade.  They  regress  in  an  oppo- 
site direction  to  that  taken  by  the  first  F2  hooded  young.  Thus  the 
original  hooded  ancestor  ( 9  5513)  was  of  grade  4.25.  The  grade  of 
hooded  young  expected  from  such  animals  is  3.84.  What  she  produced 
in  F2,  following  a  cross  with  the  wild  male,  was  young  of  mean  grade 
3.05.  Seven  of  these  of  mean  grade  2.95  produced  a  second  F2  contain- 
ing hooded  young  of  mean  grade  3.47.  This  is  a  reversed  regression  of 
0.52  on  the  grade  of  their  actual  hooded  grandparents,  or  of  0.42  on  the 
group  from  which  their  grandparents  were  chosen.  Their  mean  lies 
about  midway1  between  that  which  would  have  been  expected  from 
the  original  hooded  female  (5513)  had  no  crossing  with  wild  rats 
occurred  and  that  which  was  observed  in  the  first  F2. 

1In  The  Scientific  Monthly  (Jan.  1916)  I  have  stated  that  a  second  cross  showed  "a  return  to 
about  what  the  selected  race  would  have  been  had  no  crossing  at  all  occurred."  This  is  obviously 
inaccurate  and  should  be  corrected.  It  rests  on  a  comparison  with  the  combined  average  of  both 
the  older  and  the  more  recent  experiments. 


166  INHERITANCE    IN   RATS. 

Obviously  these  facts  do  not  harmonize  with  the  assumption  that 
the  regression  observed  in  the  first  F2  was  due  to  loss  of  modifying  fac- 
tors accumulated  during  the  ten  preceding  generations  of  selection; 
for  no  further  loss  occurs  in  the  second  F2.  On  the  other  hand,  a 
partial  recovery  is  made  of  what  was  lost  in  the  first  F2.  This  suggests 
the  idea  that  that  loss  may  have  been  due  to  physiological  causes  non- 
genetic  in  character,  such  as  produce  increased  size  in  racial  crosses;  for 
among  guinea-pigs  (as  among  certain  plants)  it  has  been  found  that  Fj. 
has  an  increased  size  due  to  vigor  produced  by  crossing  and  not  due  to 
heredity  at  all.  This  increased  size  persists  partially  in  F2,  but  for  the 
most  part  is  not  in  evidence  beyond  FV  I  would  not  suggest  that  the 
present  case  is  parallel  with  this,  but  it  seems  quite  possible  that  similar 
non-genetic  agencies  are  concerned  in  the  striking  regression  of  the  first 
F2  and  the  subsequent  reversed  regression  in  the  second  F2. 

Whatever  its  correct  explanation  may  be,  the  fact  of  the  reversed 
regression  in  a  second  F2  is  very  clear,  as  other  cases  than  those  already 
discussed  will  show. 

A  hooded  rat  of  grade  +4  and  generation  10,  c?6348,  had  by  a  wild 
female  several  young  of  the  character  already  described  for  the  young 
of  9  5513.  These,  mated  brother  with  sister,  produced  a  first  F2  (table 
141)  of  90  rats,  22  of  which  were  hooded,  68  being  non-hooded,  again 
a  good  1 : 3  ratio.  The  hooded  young  ranged  from  +2  to  +4  in  grade, 
their  mean  being  3.28.  Of  the  22  hooded  individuals,  1  male  and  7 
females  were  mated  with  wild  rats  to  obtain  a  second  F1;  and  the 
second  FI  animals  were  then  mated  brother  with  sister  to  obtain  the 
desired  second  F2.  The  character  of  this  is  shown  family  by  family  in 
table  143.  It  contained  497  individuals,  of  which  121  were  hooded 
and  376  non-hooded,  a  ratio  of  1 : 3.1.  The  weighted  mean  of  the  8 
selected  grandparents  is  2.93,  which  is  0.35  below  the  mean  of  the  22 
first  F2  hooded  animals  which  they  represent.  The  mean  of  the  second 
F2  hooded  young  is  3.22,  which  indicates  a  reversed  regression  of  0.29 
on  the  grade  of  the  grandparents,  but  shows  no  significant  difference 
from  the  mean  of  the  grandparental  group  (3.28). 

All  except  one  of  the  8  families  classified  in  table  143  show  unmis- 
takably the  reversed  regression.  This  exceptional  family  consists  of 
the  grandchildren  of  9  9747.  They  have  a  mean  grade  of  2.90,  sub- 
stantially the  same  as  that  of  the  entire  group  of  grandparents  but  con- 
siderably lower  than  that  of  their  own  hooded  grandmother.  Appa- 
rently she  did  not  come  up  genetically  to  her  phenotypic  grade.  This 
the  other  grandparents  of  the  group  did.  For  those  of  lowest  grade 
(2, 2f )  produced  lower-grade  hooded  grandchildren  than  did  the  grand- 
parents of  highest  grade  (3|,  4),  as  was  found  to  be  the  case  also,  in 
table  142. 

We  may  next  trace  the  inheritance  of  the  hooded  character  through 
a  third  but  smaller  family  produced  by  two  successive  crosses  with  wild 


HOODED   CROSSED   WITH   WILD.  167 

rats,  the  hooded  character  in  this  case  being  derived  from  96955, 
grade  +4,  generation  12.  The  character  of  her  first  F2  descendants  is 
shown  in  table  141.  They  consist  of  5  hooded  and  27  non-hooded 
individuals.  The  mean  grade  of  the  hooded  young  is  3.51,  but  the 
number  of  these  young  is  too  small  to  make  this  mean  of  much  signifi- 
cance. One  of  the  hooded  young  (cT9660,+3f )  was  mated  with  a  wild 
female  to  secure  a  second  F!  generation  and  from  this  in  due  course  was 
produced  the  second  F2  generation  (table  144) .  It  consisted  of  21  hooded 
and  44  non-hooded  young.  The  hooded  young  showed  the  usual  range 
(2  to  4).  Their  mean  grade  was  3.50,  substantially  identical  with  that 
of  the  first  F2  animals,  but  0.25  below  that  of  the  actual  hooded  grand- 
parent. This  family  history  is  less  satisfactory  than  the  two  already 
discussed  because  of  the  smaller  numbers  which  it  includes.  It  con- 
tains nothing  contradictory  to  the  interpretation  already  given,  though 
reversed  regression  is  not  in  this  case  in  evidence. 

In  two  cases  FI  females  could  not  be  mated  with  brothers  and  so 
mates  were  taken  from  other  families.  Thus  "  mixed  FI  matings" 
were  made  between  children  of  5513  and  6600  and  children  of  5513  and 
6955.  (See  table  141.)  The  former  mating  produced  3  hooded  and 
12  non-hooded  "first"  F2  young;  the  latter  produced  2  hooded  and  5 
non-hooded  "first"  F2  young.  The  grade  of  the  hooded  young  pro- 
duced by  these  mixed  matings  was  not  different  from  that  of  brother- 
sister  matings,  so  far  as  the  small  numbers  permit  one  to  judge.  One 
of  these  mixed  matings  was  carried  into  a  second  F2  generation.  The 
first  F2  hooded  cT9711,  +3|,  was  mated  with  a  wild  female,  and  the 
young  were  bred,  brother  with  sister,  producing  16  hooded  and  33  non- 
hooded  young.  (See  table  144.)  The  mean  grade  of  the  16  hooded 
young  was  3.28,  nearly  the  same  as  that  of  the  first  F2  hooded  grand- 
parent. No  additional  regression  through  loss  of  modifiers  (or  other 
agency)  is  here  in  evidence.  The  result  is  the  same  as  that  observed 
in  families  wholly  unmixed.  The  attention  of  my  pure-line  critics, 
who  think  that  in  our  mass-selection  experiments  insufficient  attention 
has  been  given  to  individual  pedigrees,  is  particularly  directed  to  the 
foregoing  case. 

Having  now  discussed  each  family  history  separately,  we  may  com- 
bine all  the  second  F2  families  in  one  table,  in  order  to  get  a  clearer 
impression  of  the  results  as  a  whole.  (See  table  145.)  The  second  F2 
generation  thus  combined  includes  256  hooded  and  749  non-hooded 
individuals,  a  ratio  of  1 :  2.9,  an  unmistakable  mono-hybrid  Mendelian 
ratio.  The  mean  grade  of  the  hooded  individuals  is  3.34.  The 
weighted  mean  grade  of  their  hooded  grandparents  was  3.02,  which 
indicates  a  reversed  regression  of  0.32  for  the  entire  second  F2  group  of 
hooded  animals. 

Classified  according  to  the  grade  of  the  (first  F2)  grandparent,  they 
show  a  correlation  between  grade  of  grandparent  and  grade  of  grand- 


168  INHERITANCE   IN   RATS. 

child.  The  lower-grade  grandparent  has  lower-grade  hooded  grand- 
children, and  the  higher-grade  grandparent  has  higher-grade  hooded 
grandchildren.  This  shows  that  the  variation  in  grade  is  (in  part  at 
least)  genotypic.  As  the  experiment  yields  no  evidence  that  the  varia- 
tion in  the  hooded  character  is  due  to  independent  modifying  factors, 
there  remains  no  alternative  to  the  conclusion  that  the  single  genetic 
Mendelian  factor  concerned  fluctuates  in  genetic  value.  Fluctuation 
accordingly  is  not  exclusively  phenotypic,  as  DeVries  and  Johannsen 
have  thought,  but  may  be  genetic  also.  Hence  racial  changes  may  be 
effected  through  selection  by  the  isolation  of  genetic  fluctuations,  as  well 
as  by  the  isolation  of  mutations.  Moreover,  genetic  fluctuation  makes 
possible  progressive  change  in  a  particular  direction,  repeated  selection 
attaining  results  which  it  would  be  quite  hopeless  to  seek  by  any  other 
means. 

A  SECOND  REPORT  ON  MASS  SELECTION  OF  THE 
HOODED  PATTERN  OF  RATS. 

The  experiments  in  selection  for  the  modification  of  the  hooded  pat- 
tern of  rats,  when  reported  on  by  Castle  and  Phillips  in  1914,  had  been 
carried  through  13  generations.  Since  then  the  experiments  with  the 
same  selected  races  have  been  carried  through  3  or  4  additional  genera- 
tions, the  results  of  which  will  now  be  described.  Additional  records  have 
also  been  obtained  for  certain  of  the  generations  reported  on  by  Castle 
and  Phillips,  which  may  now  be  combined  with  those  previously  pub- 
lished. Thus,  revised  data,  based  on  larger  totals,  may  be  given  for 
generations  12  and  13  of  the  plus-selection  series  and  for  generation  13  of 
the  minus-selection  series.  These  do  not  materially  change  the  results 
previously  obtained,  but  add  to  their  trustworthiness.  The  additional 
generations  of  selection  show  a  continued  progressive  movement  of  the 
racial  character  in  the  direction  of  the  selection  and  indicate  the  exist- 
ence of  no  natural  limit  to  the  progress  which  selection  can  make  in 
changing  the  hooded  character. 

For  details  concerning  the  earlier  history  of  the  experiments  and  the 
methods  of  grading  the  animals  the  reader  is  referred  to  the  publica- 
tion of  Castle  and  Phillips.  The  grading  scale  (exclusive  of  the  newer 
and  more  extreme  grades)  is  reproduced  in  figure  35,  plate  7.  Atten- 
tion may  be  called  to  the  fact  that  the  entire  selection  series,  both  plus 
and  minus,  consist  of  animals  descended  from  an  original  stock  of  less 
than  a  dozen  individuals.  These  descendants  number  more  than  33,000. 
In  their  ancestry,  since  the  beginning  of  the  selection  experiment,  not 
a  single  cross  out  of  the  race  has  occurred.  At  the  same  time  no  effort 
has  been  made  to  avoid  inbreeding.  Brother  and  sister  and  cousin 
matings  are  frequent  in  our  records.  Under  these  circumstances  it  is 
inevitable  that  the  selected  races  should  have  become  much  "inbred." 


MASS   SELECTION.  169 

Our  critics  with  a  leaning  toward  the  "pure-line"  idea  have  insisted 
that  nothing  but  brother-sister  matings  should  have  been  employed  in 
our  experiments.  We  have  several  times  endeavored  to  carry  forward 
certain  high-grade  families  on  this  basis,  but  have  been  unable  to  secure 
large  enough  numbers  of  offspring  to  make  this  possible;  but  we  have 
in  several  cases  produced  families  of  considerable  size,  descended  exclu- 
sively from  a  single  pair  of  ancestors — notably  in  the  case  of  our  pure 
"mutant"  race  and  in  a  race  descended  from  one  hooded  and  one  wild 
rat,  which  race  was  continued  through  8  filial  generations.  (See  p.  21, 
Castle  and  Phillips.)  It  would  have  been  impossible,  in  these  and  other 
races,  to  make  as  rapid  progress  as  we  secured  through  selection  in  our 
two  principal  races,  for  when  only  brother-sister  matings  are  permitted, 
it  often  happens  that  a  mate  of  proper  grade  can  not  be  secured  for  an 
individual  among  its  own  brothers  and  sisters,  though  such  a  mate 
may  be  found  among  its  cousins  or  more  remote  relatives.  It  being  our 
first  object  to  test  the  effectiveness  of  selection,  we  have  made  selec- 
tion of  any  individual  within  the  group  (series  or  family  with  which  we 
were  dealing)  regardless  of  relationship,  making  the  selection  as  rigid 
as  the  maintenance  of  a  stock  of  considerable  size  would  permit.  More 
than  once  we  have  crossed  the  danger-line  in  advancing  the  standard 
of  selection  to  such  an  extent  that  only  small  numbers  of  parents  came 
up  to  it;  more  than  once  we  have  had  to  relax  our  standard  temporarily 
in  order  to  keep  the  race  alive. 

That  the  long-continued  inbreeding  of  our  selected  races  has  affected 
their  vigor  and  fecundity  is  unquestionable.  It  is  shown  by  the  fact 
that  the  plus  and  minus  races,  which  had  a  common  origin  many 
generations  ago  and  have  ever  since  been  bred  in  the  same  room  and 
under  identical  conditions,  if  crossed  with  each  other,  produce  offspring 
of  much  greater  vigor  and  fecundity  than  either  parent  strain.  In  this 
our  observations  on  the  effects  of  inbreeding  are  entirely  in  harmony 
with  those  of  Darwin,  Bos,  Weismann,  and  of  breeders  of  farm  animals 
quite  generally.  Miss  King  is  credited  with  the  view  that  inbreeding 
of  rats  may  increase  their  size,  vigor,  and  fecundity,  but  this  is  cer- 
tainly contrary  to  common  experience  with  these  and  other  animals. 
It  is  probably  true  that  under  inbreeding  it  is  possible,  in  exceptional 
cases,  to  isolate  a  strain  relatively  immune  to  ill  effects  from  inbreeding 
(like  Darwin's  "Hero"  morning-glory)  or  so  inherently  vigorous  that 
it  succeeds  in  spite  of  inbreeding.  But  it  is  very  doubtful  whether 
inbreeding  of  itself  affects  vigor  other  than  disadvantageously.  It  is  a 
sufficient  test  to  cross-breed  an  inbred  strain,  in  order  to  ascertain 
whether  the  inbreeding  has  increased  or  impaired  its  vigor. 


170  INHERITANCE    IN    RATS. 

PLUS  AND  MINUS-SELECTION  SERIES. 

The  plus-selection  experiment,  when  described  by  Castle  and  Phil- 
lips, had  been  carried  through  13  generations,  but  the  last  2  genera- 
tions were  incomplete.  The  number  of  offspring  included  in  genera- 
tion 12  (table  146)  has  now  been  raised  from  590  to  682  and  the  number 
of  offspring  included  in  generation  13  (table  147)  has  been  raised  from 
194  to  529.  The  mean  grade  of  the  parents  for  generation  12  has 
advanced  from  4.09  to  4.10;  that  of  the  offspring  has  fallen  from  3.94 
to  3.93.  Neither  of  these  changes  is  of  significant  size.  The  correla- 
tion is  now  found  to  be  0.168  instead  of  0.161. 

In  generation  13  (table  147)  the  changes  are  greater,  as  might  be 
expected  from  the  greater  change  in  the  number  of  observations.  The 
mean  of  the  parents  is  now  4.13  (formerly  4.22) ;  that  of  the  offspring  is 
3.94  (instead  of  3.88).  The  correlation  is  0.117,  as  compared  with 
0.132,  the  value  previously  obtained. 

Generation  14  (table  148)  includes  1,359  offspring  of  mean  grade 
4.01.  They  are  descended  mostly  from  parents  of  grade  +4  or  higher, 
mean  4.14. 

Generation  15  (table  149)  includes  3,690  individuals,  more  than  have 
been  produced  hi  any  other  generation  of  the  series.  The  mean  grade 
of  the  parents  was  in  this  generation  advanced  about  a  quarter  grade  to 
4.38;  that  of  the  offspring  advanced  a  little,  to  4.07. 

Generation  16  (table  150)  was  also  large,  including  1,690  offspring. 
The  grade  of  the  parents  was  again  advanced  a  little  to  4.45;  that  of 
the  offspring  followed  a  similar  amount,  to  4.13. 

In  the  three  generations  (14  to  16)  which  have  been  added  since  the 
last  report,  the  grade  of  the  selected  parents  has  been  advanced  by 
0.32,  from  4.13  to  4.45;  that  of  the  offspring  has  advanced  0.19,  from 
3.94  to  4.13  (the  mean  grade  of  the  parents  three  generations  earlier). 

The  upper  limit  of  variation  of  the  offspring  has  meanwhile  advanced 
from  5.25  to  5.87,  the  highest  grade  being  found  in  a  rat  black  all  over 
except  for  a  few  white  hairs  on  the  chest.  This  rat  has  produced  a 
few  offspring  of  almost  as  high  grade,  though  the  most  of  his  young 
are  of  much  lower  grade. 

In  the  minus-selection  series,  generation  13,  in  our  previous  report, 
contained  571  offspring.  This  number  has  now  been  raised  to  1,006 
(table  151),  the  mean  grade  of  both  parents  and  offspring  being  prac- 
tically unchanged  by  the  additional  young  recorded.  The  parents  are 
of  mean  grade  —2.49,  the  offspring  of  mean  grade  —2.40. 

In  the  next  generation  (14)  the  offspring  number  717,  their  mean 
grade  being  —2.48,  that  of  the  selected  parents  being  —2.64.  (See 
table  152.) 

Generation  15  includes  1,438  young  of  mean  grade  —2.54.  The 
mean  grade  of  the  parents  is  —2.65.  (See  table  1530  N* 


MASS   SELECTION.  171 

Generation  16  is  the  largest  in  the  minus-selection  series.  It  includes 
1,980  young  of  mean  grade  —2.63.  The  grade  of  the  parents  is  —2.79. 
(See  table  154.) 

Generation  17  (table  155)  includes  868  young  of  mean  grade  —2.70. 
The  grade  of  their  parents  is  —2.86. 

Four  generations  of  selection  have  thus  been  added  to  the  minus 
series  as  it  stood  at  the  last  report.  The  mean  grade  of  the  parents  has 
been  advanced  from  —2.49  to  —2.86;  that  of  the  offspring  from 
—2.40  to  —2.70,  the  former  is  an  advance  of  0.37,  the  latter  of  0.30. 
In  the  plus  series  the  corresponding  changes  for  one  less  generation  of 
selection  (three),  were  0.32  and  0.19,  respectively.  In  both  series  a 
change  in  the  mean  of  the  offspring  attends  that  in  the  parents,  coin- 
ciding with  it  in  character  but  not  quite  equaling  it  in  amount. 

The  lagging  behind  of  the  offspring,  as  compared  with  their  selected 
parents,  gives  a  good  illustration  of  regression,  the  phenomenon  made 
familiar  by  Galton's  researches,  but  explained  away  by  Johannsen  as 
due  to  a  sorting-out  action  of  selection  on  mixed  races.  The  extent 
to  which  in  these  experiments  the  offspring  lag  behind  their  parents 
or  "regress  on  their  parents"  is  indicated  in  each  table  in  the  column 
headed  "  regression."  Tables  146  and  150  illustrate  particularly  well 
how  the  offspring  regress  toward  the  general  average  of  the  race  for  the 
time  being.  The  offspring  of  parents  substantially  the  same  grade  as 
the  general  average  of  the  race  show  no  regression;  the  offspring  of 
parents  below  this  average  show  regression  upward  (indicated  hi  the 
tables  by  the  minus  sign);  the  offspring  of  parents  above  the  racial 
average  show  regression  downward,  the  amount  of  the  regression  increas- 
ing with  the  aberrant  character  of  the  parents. 

If  one  examines  either  selection  series  as  a  whole  (compare  Castle 
and  Phillips),  he  will  notice  that  the  point  (toward  which  regression 
occurs)  changes  with  the  progress  of  the  selection.  At  the  beginning 
of  the  plus-selection  series  regression  was  toward  a  grade  of  about 
4-1.75  (see  table  1,  Castle  and  Phillips);  after  about  15  generations 
of  plus  selection  it  has  advanced  to  +4.00.  (See  tables  148  to  150.) 
At  the  beginning  of  the  minus-selection  series,  regression  occurred 
toward  a  grade  of  0  to  —1  (Castle  and  Phillips,  tables  16  and  17);  in 
generation  17  (table  155)  regression  is  apparently  toward  grade  —2.62. 
These  grades  toward  which  regression  occurs  represent  points  of  racial 
equilibrium  or  stability  at  which  the  race  would  tend  to  remain  in  the 
absence  of  further  selection,  but  these  points  of  equilibrium  are  capable 
of  being  moved  either  up  or  down  the  scale  of  grades  at  the  will  of  the 
breeder,  provided  he  has  patience  and  persistency  and  will  select 
repeatedly. 

Regression  indicates  that  there  is  not  complete  agreement  between 
the  somatic  and  the  genetic  character  of  the  parents  selected.  But  the 
steady  movement  (in  the  direction  of  the  selection)  of  the  point  of 


172  INHERITANCE    IN   RATS. 

equilibrium  toward  which  regression  occurs  serves  to  show  that  geno- 
typic  as  well  as  phenotypic  fluctuations  occur  in  the  material  on 
which  selection  is  brought  to  bear.  DeVries  and  Johannsen  have 
damned  the  word  fluctuation  by  ascribing  to  it  purely  phenotypic  sig- 
nificance. Is  it  not  worth  while  to  rescue  the  term  from  its  present 
odious  position,  since  it  is  clear  that  variation  having  a  genetic  basis 
may  in  every  way  resemble  somatic  fluctuation,  except  in  its  behavior 
under  selection?  Fluctuation  may  conceivably  be  either  somatic  or 
genetic  or  both.  No  one,  in  advance  of  actual  experiment,  can  tell 
what  its  nature  is  in  a  particular  case.  In  the  case  under  discussion 
the  fluctuation  is  obviously  partly  somatic  and  partly  genetic.  The 
somatic  fluctuation  occasions  regression,  the  genetic  fluctuation  per- 
mits a  change  (under  selection)  of  the  point  toward  which  regression 
occurs — that  is,  in  the  general  average  of  the  race. 

Tables  156  and  157  show  (generation  by  generation)  the  progress 
made  by  selection  in  modifying  the  racial  character.  It  will  be 
observed  that  as  the  mean  advances  in  the  direction  of  the  selection 
both  the  upper  and  the  lower  limits  of  variation  move  in  the  same 
direction.  The  amount  of  the  variation  as  measured  by  the  standard 
deviation  is  less  in  the  last  half  of  the  experiment  than  in  the  first  half. 
It  is  also  steadier,  owing  in  part  doubtless  to  the  fact  that  the  numbers 
are  larger,  and  in  part  to  a  more  stable  genetic  character  of  the  selected 
races.  But  the  genetic  variability  is  plainly  still  large  enough  to  per- 
mit further  racial  modification  and  there  is  no  indication  that  it  will 
cease  until  the  hooded  character  has  been  completely  selected  out  of 
existence,  producing  at  one  extreme  of  the  series  all-black  rats,  and  at 
the  other  end  of  the  series  black-eyed  white  rats. 


FURTHER  OBSERVATIONS  ON  THE  "MUTANT"  SERIES. 

Castle  and  Phillips  described,  under  the  name  "mutants,"  2  rats 
of  the  plus-selection  series  of  very  high  grade.  They  proved  to  be 
heterozygotes  between  the  average  condition  of  the  plus-selected  race 
at  that  tune,  about  +3.75,  and  a  new  condition,  not  previously  known 
in  our  hooded  races,  but  resembling  that  seen  hi "  Irish  "  rats,  which  are 
black  all  over  except  for  a  white  spot  on  the  belly  and  would  be  classed 
on  our  grading  scale  as  about  +5£.  In  later  generations  we  secured 
animals  homozygous  for  the  darker  condition  just  described  (that  of 
Irish  rats).  The  homozygous  "mutant"  race  proved  to  be  very  stable 
hi  color-pattern,  varying  only  from  5|  to  5f,  with  a  majority  of  ani- 
mals graded  5|.  Attempts  to  alter  the  modal  condition  of  the  race 
by  selection  have  thus  far  proved  futile  because  of  our  inability  to 
increase  the  race  sufficiently  to  afford  a  basis  for  selection.  Its  inbred- 
ness  and  its  feebleness  are  perhaps  causally  related. 

The  suggestion  was  made  that  the  change  from  our  plus-selected 
race,  which  had  occurred  hi  the  mutant  stock,  might  be  due  to  some 
supplementary  modifying  factor,  not  to  a  change  in  the  hooded  factor 
itself.  If  so,  a  cross  with  a  race  lacking  the  hooded  factor  or  its  "modi- 
fiers" might  serve  to  demonstrate  then*  distinctness  by  separating  one 
from  the  other.  A  wild  race  seemed  best  suited  for  a  test  of  this 
hypothesis,  since  it  would  be  free  from  suspicion  on  the  possible  ground 
of  harboring  either  the  hooded  pattern  or  its  supposed  modifier,  which 
had  converted  the  hooded  pattern  into  the  mutant.  It  was  to  be 
expected,  if  the  hypothesis  were  correct,  that  the  mutant  character 
was  hooded  plus  modifier;  that  then  a  cross  with  wild  should  produce 
in  F2  hooded  young  (lacking  the  modifier)  as  well  as  mutants  and  selfs. 
But  if  the  mutant  race  had  arisen  through  a  change  in  the  hooded  factor 
itself,  then  the  cross  should  produce  only  mutants  and  selfs,  without 
hooded  young  in  F2.  Crosses  have  now  been  made  on  a  sufficient  scale 
to  show  beyond  question  the  correctness  of  the  latter  alternative,  which 
is  entirely  in  harmony  also  with  the  results  described  in  the  preceding 
parts  of  this  paper. 

Six  homozygous  "mutant"  females  of  grade  +5^  were  mated  with 
wild  males  of  the  same  race  described  in  Part  I.  They  produced  46 
young,  all  gray  like  wild  rats  and  of  grades  as  follows: 

Grade 5£        5f        5|         6 

No 1         15          7         23 

Exactly  half  of  the  46  F!  rats  bore  no  white  spot,  i.  e.,  were  of  grade 
+6.  Seven  more  bore  only  a  few  white  hairs  (grade  5|) .  The  remain- 
der were  very  similar  to  the  mutant  parent  in  grade. 

Several  matings  were  made  of  the  Fx  rats,  brother  with  sister,  which 
produced  212  F2  young.  About  a  quarter  of  these  were  black  (non- 
173 


174  INHERITANCE   IN   RATS. 

agouti),  the  rest  being  gray  (agouti).  Both  sorts  included  about  equal 
numbers  of  individuals  with  and  without  white  spots.  No  difference 
was  observed  in  this  respect  between  the  progeny  of  spotted  and  of 
unspotted  parents.  Table  158  shows  the  F2  young  grouped  family  by 
family  according  to  grade.  Three  of  the  four  families  are  descended 
from  a  single  mutant  grandparent;  the  fourth  family  is  descended 
from  two  different  mutant  grandparents  which  were  bred  simultane- 
ously to  the  same  wild  male  in  the  same  cage.  The  10  F2  young  of 
this  family  may  have  been  produced  either  by  full  brother  and  sister, 
or  by  half-brother  and  half-sister;  it  is  uncertain  which.  All  other 
F2  young  were  produced  by  brother-sister  matings. 

It  will  be  observed  that  the  F2  young  (table  158)  which  are  white- 
spotted  are  in  no  case  hooded.  Their  range  of  variation  does  not  fall 
beyond  that  of  the  uncrossed  mutant  race.  It  is  certain,  therefore, 
that  the  "mutant"  condition  is  not  hooded  plus  an  independent  Mendel- 
ian  modifier.  It  is  a  changed  form  of  white-spotting,  alternative  to  the 
form  of  spotting  found  in  the  race  from  which  it  was  derived  (the  plus- 
selection  series,  generation  10).  It  is,  without  much  doubt,  also  alter- 
native to  the  self  condition  of  wild  rats,  though  fluctuation  in  grade  ob- 
scures the  segregation,  which  may,  very  likely,  be  imperfect.  This  serves 
to  confirm  the  general  conclusion  that  throughout  the  entire  series  of 
experiments  with  the  hooded  pattern  of  rats  we  are  dealing  with  quan- 
titative variations  hi  one  and  the  same  genetic  factor. 


GAMETIC  COUPLING  IN  YELLOW  RATS. 

Two  yellow-coated  varieties  of  the  Norway  rat  (Mus  norvegicus) 
made  their  appearance  as  sports  or  mutations  in  England  a  few  years 
since  (Castle,  1914)  and  are  now  recognized  as  distinct  varieties  by 
fanciers.  Both  are  similar  in  appearance  except  for  the  eye  color.  In 
one  variety  the  eye  is  pink,  showing  under  gross  inspection  only  the 
color  of  the  blood  in  the  retina.  In  the  other  variety  the  eye  is  a 
reddish-black,  owing  to  the  combined  effect  of  the  red-colored  blood 
and  the  black-pigmented  retina.  Since  the  retinal  pigment  is  much  less 
in  this  variety  than  in  rats  with  gray  or  black  coats,  the  eye  is  redder. 
It  will  be  convenient  to  distinguish  the  dark-eyed  yellow  variety  as 
red-eyed,  reserving  the  name  black-eyed  for  gray  or  black  rats. 

In  the  coats  of  both  the  pink-eyed  and  the  red-eyed  varieties  of 
yellow  rats  black  pigment  is  very  feebly  developed.  It  is  in  fact  of  a 
pale  cream  color.  But  the  true  yellow  pigment  seen  on  the  tips  of  the 
hairs  of  gray  rats  is  retained  in  full  intensity  in  the  yellow  varieties. 
For  this  reason  agouti  varieties  of  yellow  rats  are  much  brighter-colored 
than  non-agouti  varieties.  A  non-agouti  yellow  variety  has  fur  cream- 
colored  throughout  its  length;  the  corresponding  agouti  variety  has  fur 
of  this  same  cream  color  at  its  base,  where  the  fur  of  gray  rats  is  black- 
pigmented,  but  the  hair-tips  are  of  a  bright  yellow  color  of  exactly  the 
same  shade  as  the  hair-tips  of  gray  rats.  Hence  it  is  clear  that  in 
these  yellow  varieties  of  rats  a  genetic  factor  for  black  pigmentation  has 
been  affected  without  any  apparent  change  in  the  genetic  apparatus  for 
producing  ordinary  yellow  pigment. 

This  is  quite  different  from  the  genesis  of  yellow  coat  in  most  ro- 
dents— for  example,  in  guinea-pigs  and  rabbits — in  which  black  pig- 
ment is  not  apparently  changed  in  character  but  merely  in  distribution, 
being  "restricted"  chiefly  to  the  eye.  In  the  yellow  varieties  of  rats 
black  pigment  seems  to  be  affected  in  the  same  way  as  in  the  pink-eyed 
variety  of  guinea-pigs  and  mice,  viz,  to  be  greatly  weakened  without 
affecting  in  the  least  the  development  of  yellow  pigment.  The  genetic 
behavior  as  well  as  the  appearance  of  the  pink-eyed  yellow  variation  in 
rats  is  in  every  way  parallel  with  the  behavior  of  the  variations  known 
by  the  same  name  hi  mice  and  guinea-pigs.  But  red-eyed  yellow  in 
rats  is  a  genetically  distinct  variation,  as  we  shall  presently  see.  In  no 
other  mammal  does  there  occur  a  parallel  variation,  so  far  as  I  know. 
Both  red-eyed  yellow  and  pink-eyed  yellow  were  found  to  be  recessive 
Mendelian  variations  in  crosses  with  black-eyed  rats.  From  a  cross 
between  black-eyed  and  red-eyed  an  F2  generation  of 4  609  rats  was 
raised,  of  which  452  were  black-eyed  and  157  red-eyed;  expected, 
457  : 152.  From  a  cross  between  black-eyed  and  pink-eyed  rats,  cer- 
tain F!  females  were  back-crossed  with  a  pure  pink-eyed  male.  They 
produced  46  black-eyed  and  39  pink-eyed ;  expected,  42  of  each. 

175 


176  INHERITANCE   IN   RATS. 

The  pink-eyed  yellow  and  red-eyed  yellow  of  rats  are  complementary 
loss  variations;  for  when  the  two  varieties  are  crossed  with  each  other 
they  produce  FX  offspring  which  are  either  gray  or  black  pigmented, 
according  as  their  yellow  parents  did  or  did  not  transmit  the  agouti 
factor.  These  F!  reversionary  grays  or  blacks  are  paler  in  pigmenta- 
tion than  ordinary  gray  or  black  rats,  indicating  that  neither  character 
in  a  heterozygous  form  is  the  full  complement  of  the  other.  But  it  is 
evident  that  in  homozygous  form  each  is  the  full  complement  of  the 
other,  since  in  F2  and  later  generations  grays  and  blacks  of  full  intensity 
are  obtained. 

The  F!  black-eyed  animals  (blacks  or  grays)  obtained  by  crossing 
pink-eyed  yellows  with  red-eyed  yellows,  if  mated  with  each  other,  pro- 
duce an  F2  generation  containing  (1)  black-eyed  young  (black  or  gray), 
(2)  red-eyed  yellow  young,  and  (3)  pink-eyed  yellow  young.  We  have 
obtained  thus  far  324  such  F2  young,  of  which  162  were  of  class  (1),  90 
of  class  (2),  and  72  of  class  (3). 

If,  as  suggested,  red-eyed  yellow  and  pink-eyed  yellow  are  due  to 
mutually  independent  Mendelian  factors,  then  F2  should  contain  four 
classes  instead  of  the  apparent  three;  wherefore  it  seemed  probable 
that  one  of  the  three  classes  was  really  composite  and  that  the  three 
should  be  as  9:3:4.  On  this  basis  the  F2  expectation  would  be 
182  : 61 : 81  instead  of  the  observed  162  :  72  :  90.  Hence  there  appear 
to  be  fewer  black-eyed  young  than  are  expected.  Further,  when  we 
came  to  test  the  other  F2  classes  to  discover  which  of  them  was  com- 
posite, we  found  very  few  individuals  which  would  fall  in  the  hypotheti- 
cal fourth  class  transmitting  both  pink-eyed  and  red-eyed  yellow  in  the 
same  gamete.  Instead  of  1  hi  16  as  expected,  we  have  been  able  to 
discover  a  much  smaller  number  of  double  recessives.  Both  a  defi- 
ciency in  double  recessives  and  a  deficiency  in  double  dominants  (the 
black-eyed  class),  which  have  been  observed  among  the  F2  rats,  would 
be  expected  if  pink-eyed  yellow  and  red-eyed  yellow  are  due  to  "  linked 
genes,"  i.  e.,  to  factors  located  near  each  other  in  the  germ-plasm.  For 
in  the  cross  under  consideration  each  form  of  yellow  enters  the  F! 
zygote  in  a  different  gamete.  Hence,  in  the  gametes  arising  from  such 
zygotes  we  should  expect  the  two  forms  of  yellow  to  show  mutual 
repulsion.  If  they  did  so,  then  the  gametes  formed  by  FX  zygotes,  of 
the  four  possible  combinations,  RP,  Rp,  rP,  and  rp,  would  not  be 
equally  numerous,  but  Rp  and  rP  should  be  more  numerous  than  RP 
and  rp.  That  this  is  true  is  indicated  by  the  facts  presently  to  be 
stated.  To  test  the  gametic  composition  of  the  F2  yellows,  those  which 
were  red-eyed  were  mated  with  pink-eyed  yellows  of  pure  race,  and 
those  which  were  pink-eyed  were  mated  with  red-eyed  yellows  of  pure 
race.  For  it  was  known  that,  since  red-eyed  yellow  is  a  recessive 
variation,  every  red-eyed  F2  yellow  must  be  homozygous  for  red-eye, 
but  conceivably  it  might  be  either  heterozygous  for  pink-eye  or  might 
lack  it  altogether.  A  cross  with  the  pure  pink-eyed  yellow  race  would 


GAMETIC    COUPLING    IN   YELLOW   RATS. 


177 


decide  between  these  possibilities.  Further,  it  was  clear  that  every 
pink-eyed  F2  yellow  must  be  homozygous  for  that  character,  which  is 
also  recessive,  but  might  be  either  homozygous  or  heterozygous  for 
red-eye  without  affecting  its  appearance,  or  might  even  lack  the  gene 
for  red-eye  altogether.  A  cross  with  pure  red-eyed  animals  would 
suffice  to  show  in  each  case  which  possibility  was  realized.  In  accord- 
ance with  this  reasoning  the  proposed  tests  have  been  made  hi  the  case 
of  45  red-eyed  and  40  pink-eyed  F2  yellows. 

Of  the  45  red-eyed  yellows  tested,  32  have  given  exclusively  black- 
eyed  young  (blacks  or  grays),  no  test  being  considered  adequate  which 
did  not  produce  4  or  more  young;  but  13  of  the  tested  animals  gave  a 
mixture  of  black-eyed  and  of  red-eyed  young  in  approximately  equal 
numbers.  The  former  group,  numbering  32,  evidently  lacked  the  gene 
for  pink-eye,  since  they  always  produced  atavists  in  crosses  with  pink- 
eyed  yellows;  the  latter  group,  numbering  13,  were  evidently  hetero- 
zygous for  pink-eye,  since  only  part  of  their  young  were  atavistic. 

Of  the  40  pink-eyed  F2  yellows  which  were  tested,  27  produced  only 
black-eyed  young;  these  evidently  lacked  the  gene  for  red-eye.  Ten 
others  produced  both  black-eyed  and  red-eyed  young,  being  evidently 
heterozygous  for  red-eye.  Three  have  produced  only  red-eyed  young, 
which  shows  them  to  be  homozygous  for  red-eye  as  well  as  for  pink-eye. 
Hence  they  are  the  double  recessives,  expected  to  be  one-sixteenth  of 
all  F2  rats  if  no  linkage  occurs,  but  less  numerous  if  linkage  occurs. 

We  are  now  in  a  position  to  estimate  the  strength  of  the  linkage 
shown.  If  we  designate  by  r  the  recessive  gene  for  red-eye,  and  by  p 
the  recessive  gene  for  pink-eye,  then  in  the  current  Mendelian  terminol- 
ogy the  following  F2  classes  are  to  be  expected  in  the  frequencies  shown, 
if  no  linkage  occurs : 


Black-eyed. 

Red-eyed. 

Pink-eyed. 

1  RRPP... 
2  RrPP  .  .  . 

IrrPP  
2  rrPp  

1  RRpp 
2  Rrpp 

2  RRPp  .  .  . 

1  rrpp 

4RrPp 

9 

3 

4 

For  the  present  we  may  pass  by  the  black-eyed  classes,  since  none  of 
these  were  individually  tested.  The  individual  tests  already  described 
have  shown  the  existence  of  the  expected  two  classes  of  red-eyed  and 
three  classes  of  pink-eyed  young,  but  in  proportions  very  different 
from  those  given  in  the  table.  Among  the  red-eyed,  instead  of  the 
expected  1  rrPP :  2  rrPp,  we  observe  32  : 13.  Among  the  pink-eyed, 
where  we  expect  1  RRpp  :  2  Rrpp :  1  rrpp,  we  observe  27  : 10  :  3.  These 
are  very  different  frequencies  from  those  expected,  and  they  strongly 
suggest  linkage.  How  strong  is  the  linkage?  We  may  estimate  it 


178 


INHERITANCE    IN    RATS. 


from  the  actual  proportions  of  the  four  possible  kinds  of  gametes  which 
the  FI  parents  produced.  With  no  linkage  these  gametes  should  be  of 
four  sorts,  all  equally  numerous,  viz,  RP  +  Rp  +  rP  +  rp.  Linkage 
would  tend  to  increase  the  proportion  of  the  two  middle  classes  (Rp 
and  rP,  the  original  combinations)  at  the  expense  of  the  extremes  (RP 
and  rp,  the  double  dominant  and  double  recessive  classes) .  The  latter 
may  be  called  "cross-over"  classes,  the  former  " non-cross-over."  In 
producing  the  85  F2  yellow  rats  which  were  tested,  twice  that  number 
of  gametes  were  concerned,  viz,  170.  From  the  demonstrated  genetic 
constitution  of  the  tested  animals,  we  can  estimate  how  many  cross- 
over and  how  many  non-cross-over  gametes  entered  into  each. 


Zygotes. 

Cross-over 
gametes. 

Non-cross-over 
gametes. 

32rrPP  
13  rrPp  

13 

64 
13 

27  RRpp  
10  Rrpp  

10 

54 
10 

3  rrpp  

6 

85 

29 

141 

The  estimated  proportion  of  cross-over  to  non-cross-over  gametes  is 
seen  to  be  29  : 141  or  1 :  4.8.  In  the  terminology  of  Bateson  and  Pun- 
nett  this  would  be  a  reduplication  series  lying  between  1:4:4:1  and 
1:5:5:1;  in  the  terminology  of  Morgan,  17  per  cent  of  the  gametes 
formed  by  Ft  individuals  are  cross-over  gametes. 

We  can  test  this  linkage  theory  in  another  way.  If  linkage  exists 
it  should  modify  the  proportions  of  the  apparent  classes  in  F2  as  well 
as  of  the  real  classes,  which  we  have  just  been  considering.  The 
apparent  classes  are  three,  viz,  black-eyed,  red-eyed,  and  pink-eyed, 
with  observed  frequencies  of  162  :  90 :  72.  If  no  linkage  exists  the 
expected  frequencies  are  182  :  61 :  81,  which  deviate  considerably  from 
the  expected  frequencies.  But  if  linkage  exists,  it  will  lessen  the  discrep- 
ancies. Linkage  of  17  per  cent  strength  will  change  the  expectations  to 
164 : 79 : 81 .  This  alteration  shows  agreement  almost  perfect  in  the  case 
of  the  black-eyed  class,  a  much  reduced  discrepancy  in  the  case  of  the 
red-eyed  class,  and  no  change  in  the  pink-eyed  class — on  the  whole  a 
much  improved  agreement  between  expected  and  observed  frequencies. 

Sturtevant  has  called  attention  to  the  fact  that  double  recessives 
could  occur  among  our  F2  animals  only  as  a  result  of  cross-overs  occur- 
ring simultaneously  in  the  gametes  of  both  parents,  a  fact  which  Wright 
and  I  considered  too  obvious  to  demand  comment  in  our  preliminary 
paper,  but  recognized  in  our  calculation  by  counting  two  cross-over 
gametes  for  every  double  recessive  zygote.  Sturtevant  has  questioned 
the  adequacy  of  our  tests  in  the  case  of  these  doubly  recessive  indi- 
viduals because  apparently  he  had  formed  the  idea,  from  studies  made 
on  insects,  that  crossing-over  could  occur  only  in  the  gametogenesis  of 


GAMETIC   COUPLING   IN   YELLOW   RATS.  179 

one  sex.  I  may  say,  therefore,  that  the  classification  of  two  animals  as 
double  recessives  made  in  our  preliminary  paper  was  based  on  tests 
which  had  produced  14  and  9  yellow  young  respectively.  The  only 
possible  alternative  classification  would  have  involved  an  expected  1 : 1 
ratio  of  black-eyed  to  red-eyed  young.  The  chances  are  overwhelm- 
ingly great  against  the  observed  results  being  departures  due  to  ran- 
dom sampling  from  this  expectation.  The  additional  case  of  a  double 
recessive  reported  in  this  paper  is  so  classified  on  tests  which,  to  the 
present  time,  have  produced  all  together  28  yellow  young.  The  num- 
ber of  young  produced  hi  each  of  the  other  tests  is  indicated  below. 
Tests  taken  to  indicate  that  the  parent  was  of  the  formula  rrPP 
produced  only  dark-eyed  young  (gray  or  black-coated),  as  follows: 

No.  of  young....  4    5    6    7    8    9     10     11     12     13     16     17     19 
Cases 244522131231       2  =  32 

Tests  showing  the  parents  to  be  of  the  formula  rrPp  gave  the  follow- 
ing numbers  in  13  tests: 

Dark-eyed  :Pink-eyed. .  .2: 6   4:2   5:4    1:5   3:3   5:3   4:6    1:5   5:5   3:4  3:2  1:5  6:3 

Pink-eyed  animals  were  classified  as  of  formula  RRpp  on  the  basis 
of  the  following  tests,  which  yielded  only  dark-eyed  young: 

No.  of  young....  4    6    7    8    9     10     11     12     13     14     15     16     18 
Cases 213222161311      2  =  27 

Pink-eyed  animals  were  shown  to  be  of  formula  Rrpp  by  the  follow- 
ing tests: 

Dark-eyed:  Red-eyed...  10: 7      8:4      1:4      7:8      6:7     5:6     3:1      4:6     4:2     8:2 

Both  red-eyed  and  pink-eyed  yellow  rats,  when  crossed  with  albinos, 
produce  an  F\  generation  consisting  exclusively  of  black-eyed  (black 
or  gray)  young.  F2  from  the  red-eyed  cross  consisted  of  black-eyed, 
red-eyed,  and  albino  young,  and  F2  from  the  pink-eyed  cross  consisted 
of  black-eyed,  pink-eyed,  and  albino  young.  If  no  linkage  occurs  the 
expectation  in  each  case  is  9  :  3  : 4,  and  we  at  first  supposed  that  this 
was  the  ratio  approximated.  But  a  summary  of  all  litters  thus  far 
obtained  indicates  a  probable  linkage  between  albinism  and  the  two 
yellow  variations. 

Thus,  red-eyed  non-agouti  yellows  mated  with  albinos  from  our  plus- 
selected  hooded  race  produced  17  black  F1  young.  These  have  given 
us  58  F2  young,  of  which  30  are  black-eyed,  18  red-eyed,  and  10  albinos. 
A  9  :  3  : 4  ratio  would  call  for  32.5  : 11 : 14.5.  It  is  evident,  therefore, 
that  we  have  too  many  red-eyed  young  and  too  few  black-eyed  and 
albinos.  Linkage  (in  this  case,  repulsion)  between  red-eye  and  albin- 
ism would  tend  to  increase  the  number  of  red-eyed  and  to  decrease 
the  number  of  black-eyed  without  changing  materially  the  expecta- 
tion for  albinos;  hence,  linkage  seems  probable.  Linkage  involving 
1  cross-over  to  3  non-cross-over  gametes,  or  25  per  cent  cross-over 


180 


INHERITANCE    IN   RATS. 


gametes,  would  give  an  expectation  of  29.9  black-eyed :  13.6  red-eyed  : 
14.5  albinos,  which  agrees  much  better  with  the  observed  numbers 
(30 : 18 : 10)  than  does  the  9:3:4  distribution.  But  if  red-eye  is 
linked  with  albinism  as  well  as  with  pink-eye,  then  albinism  and  pink- 
eye should  be  linked  with  each  other.  Apparently  such  is  the  case, 
for  three  F2  Utters  from  the  cross  pink-eye  X  albino  include  12  black, 
12  pink-eyed,  and  3  albino  young.  A  9:3:4  ratio  (expected  if  no 
linkage  occurs)  would  call  for  15  black,  5  pink-eyed,  and  7  albinos. 
Linkage  of  5  : 1  would  call  for  14  :  6  :  7,  and  perfect  linkage  would  call 
for  14 :  7 :  7.  It  is  evident  that  the  observed  numbers  of  blacks  and 
albinos  are  too  small  on  any  of  these  hypotheses,  but  the  existence  of 
linkage  would  tend  to  diminish  the  number  of  blacks  and  albinos  in 
proportion  to  the  number  of  pink-eyed,  which  is  the  nature  of  the 
deviation  observed.  To  determine  definitely  whether  linkage  really 
occurs  between  the  yellow  variations  and  albinism,  and  if  so,  what  is 
its  strength,  further  experiments  are  needed,  which  are  now  in  progress. 
It  will  also  be  desirable  to  determine  whether  the  linkage  strength  is 
the  same  in  both  sexes. 

SUMMARY. 

Two  yellow  variations  in  rats  which  have  recently  arisen  as  muta- 
tions show  mutual  repulsion  in  heredity.  When  crossed  with  each 
other  they  produce  an  F!  generation  composed  exclusively  of  rever- 
sionary dark-eyed  individuals.  The  F2  young  are  of  three  apparent 
classes,  dark-eyed,  red-eyed,  and  pink-eyed.  Their  numerical  propor- 
tions deviate  somewhat  from  the  typical  9:3:4  ratio.  Further,  the 
proportions  of  the  several  expected  classes  of  red-eyed  and  pink-eyed 
young  do  not  agree  with  those  usually  observed  hi  an  F2  Mendelian 
population.  But  hi  both  cases  the  deviations  are  largely  accounted  for 
by  the  supposition  that  the  genes  of  the  respective  yellow  variations 
are  "linked"  (hi  this  case  showing  repulsion)  and  that  the  proportion 
of  "cross-over  "  gametes  is  about  17  per  cent,  or  mother  words,  that  non- 
cross-over  gametes  are  about  4.8  times  as  numerous  as  cross-over  gametes. 

NOTE. — In  the  foregoing  discussion  it  has  been  assumed  that  the  ratio  of 
cross-over  to  non-cross-over  gametes  is  the  same  among  gametes  which  take 
part  in  producing  yellows  as  among  those  which  take  part  in  producing  black- 
eyed  individuals.  Theoretically  it  should  be  slightly  different,  as  the  following 
table  will  show: 


Ratio  cross-over 
to  non-cross-over 
gametes. 

Per  cent 
cross-over 
gametes. 

Per  cent  among 
gametes  pro- 
ducing yellows. 

Per  cent  among 
gametes  produc- 
ing black-eyed. 

1:  1 
1:2 
1:3 
1:4 
1:4-4 
1:5 
1:6 

50 
33.3 
25 
20 
18.5 
16.7 
14.3 

42.9 
29.4 
22.6 
18.4 
17.  1 
15.5 
13.4 

55.6 
36.8 
27.3 
21.6 

19.  8  -> 
17.8 
15.2 

TABLES. 


181 


TABLES. 

Table  141  shows  the  classification  of  extracted  hooded  first 
crossing  hooded  rats  of  the  plus-selected  series  with  wild  rats. 

TABLE  141. 


young  obtained  from 


Hooded  grandparents. 

Grade  of  hooded  grandchildren. 

Total 
hooded. 

Total 
non- 
hooded. 

Means 
of 
hooded. 

11 

u 

2 

21 

21 

2f 

8 

3* 

3} 

:*! 

4 

95513,  +41,  gen.  10  

1 

3 
1 

2 

1 
1 

7 
2 

8 

4 

6 
3 
1 

5 

4 
1 

1 

7 

6 
3 

1 
1 

41 
22 
5 

3 

2 

107 
68 
27 

12 
5 

3.05 
3.28 
3.51 

3.17 
3.37 

o"6348,  +4,  gen.  10  

9  6955,  +4,  gen.  12  

9  5513,  +4J,  and  9  6600,  +41, 
gen.  12  

3 

95513,   -Hi,  and   96955,   +4, 
gen.  12  

1 

1 

Totals  ....                

1 

4 

2 

2 

9 

14 

11 

12 

16 

2 

73 

219 

3.17 

Table  142  shows  the  classification  of  extracted  hooded  second  ¥2  young  obtained  from 
crossing  first  F2  hooded  rats  (table  141)  with  wild  rats.  The  hooded  grandparents  were 
themselves  grandchildren  of  9  5513,  +4|,  generation  10,  on  the  side  of  both  parents. 

TABLE  142. 


Hooded  grand- 
parents. 

Grade  of  hooded 
grandchildren. 

Total 
hooded. 

Total 
non- 
hooded. 

Means 
of 
hooded. 

2 

2J 

2i 

2f 

3 

3i 

3* 

31 

4 

99619,  +2.. 

1 
1 
2 
1 
2 
5 
1 

1 
2 
2 
4 

11 
6 

2 

i 

3 
4 

7 
8 

7 

30 

1 
4 
1 
5 

2 
5 
13 
10 
30 
22 
16 

8 
28 
24 
22 
104 
68 
42 

3.37 
3.40 
3.06 
3.62 
3.47 
3.55 
3.70 

0*9686,  +2J.   . 

1 
1 

99620,  +2i... 
99729,  +21... 

1 

1 

2 

1 

c?9727,  +3.... 
9  9728,  +3  .... 
99621,  +31... 

1 

i 

2 
1 

3 
1 

Totals  .  .  . 

1 

2 

8 

4 

6 

13 

2S 

1! 

98 

296 

3.47 

Table  143  shows  the  classification  of  extracted  hooded  second  F2  young  obtained  from 
crossing  first  Fa  hooded  rats  (table  141)  with  wild  rats.  The  hooded  grandparents  were 
themselves  grandchildren  of  cf  6348,  +4,  generation  10,  on  the  side  of  both  parents. 

TABLE  143. 


Hooded  grand- 
parents. 

Grade  of  hooded  grand- 
children. 

Total 
hooded. 

Total 
non- 
hooded. 

Means 
of 
hooded. 

If 
1 

2 

2 
1 

21 
1 

2J 

2! 

3 

3 

6 

l 

3} 

4 

34 

15 
4 

si 

6 

4 

cf9639,  +2.  ... 

1 

39 
6 
1 
27 
16 
21 
9 
2 

110 
16 
10 
76 
47 
74 
40 
3 

3.24 
3.17 
3.50 
2.90 
3.28 
3.48 
3.36 
3.87 

99704,  +2i.  .  .  . 

9  9765,  +3    .  . 

1 

99747,  +3i  
9  9703,  +3i  

1 

7 

i 

i 
i 

1 
2 
1 
1 

7 
2 
5 
2 

1 
1 
1 
1 

4 
6 
4 
2 

4 
2 

<S 
3 

1 

24 

1 
2 
2 

i 

7 

9  9705,  +3i  

99748,  +3i  

9  9796,  +4  

Totals  

2 

35 

2 

10 

2 

8 

23 

8 

121 

376 

3.22 

182 


INHERITANCE    IN   RATS. 


Table  144  shows  the  classification  of  extracted  hooded  second  Fa  young  obtained  from 
crossing  first  F2  hooded  rats  with  wild  rats.  The  hooded  grandparent,  d"9660,  +3f ,  was 
a  grandson  of  9  6955,  +4,  generation  12,  on  the  side  of  both  parents.  The  hooded  grand- 
parent, 0*9711,  +3£,  was  a  grandson,  on  the  side  of  one  parent,  of  9  5513,  +4J,  generation 
10,  and  on  the  side  of  the  other  parent,  of  96955,  +4,  generation  12.  (See  table  141.) 

TABLE  144. 


Hooded  grand- 
parents. 

Grade  of  hooded 
grandchildren. 

Total 
hooded. 

Total 
non- 
hooded. 

Means 
of 
hooded. 

2 

21 

2J 

1 
1 

2f 

1 
2 

3 

31 

3* 

8} 

4 

0*9660,  +3J... 
d"9711,  +31... 

1 

1 
2 

2 

4 

5 
4 

9 
2 

2 

1 

21 
16 

44 
33 

3.50 
3.28 

Totals  

~ 

1 

3 

3 

0 

9 

11 

3 

37 

77 

3.40 

Table  145  is  a  combination  of  tables  142  to  144,  in  which  the  second  F2  young  are  classi- 
fied according  to  the  grade  of  their  first  Fz  hooded  grandparent. 

TABLE  145. 


Grade  of 
hooded 

Grade  of  hooded  grand- 
children. 

Total 

Total 

Means 

grand- 
parents. 

1| 

2 

2* 

2k 

22 

3 

31 

3J 

3| 

4 

hooded. 

hooded. 

hooded. 

2 

1 

2 

1 

3 

6 

5 

16 

6 

1 

41 

118 

3.25 

2| 

2 

1 

2 

1 

3 

4 

12 

8 

1 

34 

90 

3.29 

3 

1 

1 

2 

4 

7 

18 

15 

5 

53 

182 

3.48 

31 

1 

7 

2 

4 

9 

6 

10 

13 

7 

59 

151 

3.22 

3i 

1 

1 

4 

9 

3 

11 

13 

4 

46 

161 

3.39 

3} 

1 

1 

1 

2 

6 

9 

2 

21 

44 

3.50 

4 

1 

1 

2 

3 

3  87 

15 

32 

27 

72 

65 

3.02 

2 

12 

4 

6 

21 

256 

749 

3.34 

Table  146  shows  the  classification  of  generation  12,  plus-selection  series.     This  is  an 
enlargement  of  table  12  of  Castle  and  Phillips. 

TABLE  146. 


Grade  of 
parents. 

Grade  of  offspring. 

Totals. 

Means. 

Regres- 
sion. 

2J 

2} 

2! 

3 

31 

3| 

3f 

4 

41 

4* 

4f 

5 

5i 

3* 
3| 
4 
4* 
41 
4f 
4* 
4f 
4| 

if 

5 

4 
3 
12 
25 
11 
3 

20 
23 
62 
106 
25 
6 
1 
3 

7 
21 
66 
91 
35 
14 
4 
4 

4 
6 
12 
30 
16 
10 
1 
3 

35 
57 
164 
267 
95 
45 
7 
11 

3.83 
3.94 
3.91 
3.87 
3.95 
4.17 
4.14 
3.91 

-.08 
-.06 
.09 
.25 
.30 
.20 
.36 
.71 

2 
5 
6 
5 
7 

2 
1 

3 
2 
3 

1 
1 

1 
1 

2 
1 

1 

2 
3 

2 

1 

1 

1 

1 

4.75 

.25 

4.10 

2 

3 

5 

58 

246 

242 

82 

25 

12 

4 

3 

682 

3.93 

.17 

TABLES. 


183 


Table  147  shows  the  classification  of  generation  13,  plus-selection  series.    This  is  an  enlarge- 
ment of  table  13  of  Castle  and  Phillips. 

TABLE  147. 


G-ade  of 
parents. 

Grade  of  offspring. 

Totals. 

Means. 

Regres- 
sion. 

2| 

8 

3} 
1 

3i 
1 

3} 
1 

4 

41 

4] 

42 

5 

H 

3i 
3| 
3i 
31 
4 
4* 
4i 
4| 
4* 
4f 
41 
4* 

3 

3.50 

0 

1 

4 
33 
11 
7 
2 
1 

3 
9 

60 
32 
23 
8 
15 
1 
3 

11 

7 
59 
33 
33 
7 
17 
2 
1 
2 

3 
4 
25 
13 
13 
6 
10 
1 

i 

1 
1 

17 
5 
1 
1 
5 

1 
3 
2 

2 
3 
1 

1 

1 
1 

i 

i 

21 
31 
205 
96 
80 
29 
50 
4 
5 
5 

4.08 
3.90 
3.90 
3.92 
3.93 
4.03 
4.05 
4.00 
3.95 
4.05 

-.33 
-.03 
.10 
.20 
.32 
.34 
.45 
.62 
.80 
.82 

i 

1 
1 

1 

2 
7 
1 

1 

i 

i 

4.13 

i 

3 

11 

61 

155 

172 

76 

32 

13 

4 

i 

529 

3.94 

.19 

Table  148  shows  the  classification  of  generation  14,  plus-selection  series. 

TABLE  148. 


Grade  of 
parents. 

Grade  of  offspring. 

Totals. 

Means. 

Regres- 
sion. 

2i 

2f 

3 

3J 

3i 

31 

4 

4i 

4| 

4f 

5 

51 

5* 

3i 
3f 
3! 
31 
4 
4* 
4i 
4* 
4i 
4f 
4f 
41 
5 
5| 
5i 

2 
2 
11 

28 
4< 
19 
6 
2 
3 

6 
9 
32 
52 
84 
74 
25 
24 
12 
11 
5 
1 

3 
4 
45 
63 
122 
72 
48 
36 
31 
13 
16 
7 

1 

12 
24 
115 
184 
306 
241 
130 
100 
101 
58 
45 
33 

3.83 
4.02 
3.90 
3.97 
3.92 
3.99 
4.04 
4.04 
4.16 
4.23 
4.17 
4.33 

-.33 
-.39 
-.15 
-.10 
.08 
.13 
.21 
.33 
.34 
.39 
.58 
.54 

7 
18 
28 
50 
56 
42 
29 
37 
15 
14 
14 

1 

5 
8 
6 

15 
8 

6 
12 
11 
8 

6 

1 

1 

2 

1 

1 
"2 

3 
2 

3 
1 

2 
3 
8 

2 
3 

1 

1 

1 

1 

2 
2 

1 

1 

1 

1 

1 

4 

1 

1 
1 

6 

4 

4.25 
4.75 

.87 
.50 

24 

1 
9 

1 
4 

1 

4.14 

1 

3 

4 

113 

335 

461 

315 

«9 

1,359 

4.01 

.13 

184 


INHERITANCE   IN   RATS. 


Table  149  shows  the  classification  of  generation  15,  plus-selection  series. 

TABLE  149. 


Grade  of 
parents. 

Grade  of  offspring. 

Totals. 

Means. 

Regres- 
sion. 

2* 

23 

3 

3i 

31 

33 

4 

41 

4* 

43 

5 

51 

51 

3J 
3{ 
4 
4* 
41 
4f 
41 
4$ 
4* 
41 
5 
51 
51 

1 

2 
1 
2 
1 
1 
1 

3 
5 

16 
29 
22 
18 
9 
3 
3 

3 
10 
58 
184 
183 
207 
99 
37 
25 
13 
1 

7 
30 
156 
670 
721 
969 
506 
237 
168 
146 
43 
18 
19 

3.57 
3.80 
3.91 
4.00 
4.02 
4.06 
4.10 
4.11 
4.22 
4.37 
4.27 
4.37 
4.36 

.18 
.07 
.09 
.12 
.23 
.31 
.40 
.51 
.53 
.50 
.73 
.75 
.89 

11 

46 
255 
296 
357 
159 
87 
38 
25 
9 
4 
2 

2 
28 
165 
165 
290 
175 
88 
58 
42 
21 
4 
10 

7 
29 
44 
71 
48 
14 
24 
34 
10 
7 
5 

i 

1 

i 

a 

8 
21 
6 
6 
6 
15 
2 
3 
1 

69 

1 

1 
3 

7 

2 
9 

12 

1 

6 

4 

2 
1 

"i 

1 

36 

11 

4 

i 

~- 

2 

4.38 

9 

108 

820 

1,289 

1,048 

293 

3,690 

4.07 

.31 

Table  150  shows  the  classification  of  generation  16,  plus-selection  series. 

TABLE  150. 


Grade  of 
parents. 

Grade  of  offspring. 

Totals. 

Means. 

Regres- 
sion. 

31 

i 

31 

4 
4 
9 

7 

33 

4 

41 

41 

n 

5 

Si 

H 

53 

51 

41 
41 
4| 

41 
4f 
43 
4* 
5 
51 

26 
34 
149 
25 
12 

64 
64 
316 
82 
50 
12 
23 
8 
1 

37 

40 
271 
69 
61 
16 
26 
25 
8 

8 
5 

58 
18 
26 
19 
8 
15 
6 

139 
149 

816 
206 
166 
66 
69 
61 
18 

4.04 
4.02 
4.08 
4.10 
4.24 
4.47 
4.21 
4.44 
4.39 

.08 
.23 
.29 
.40 
.38 
.38 
.66 
.56 
.73 

1 

9 
5 
11 
10 
3 
7 

*i 

1 
2 

4 

6 
2 
2 
1 

1 
1 
1 
2 
1 

1 
2 

1 

5 

i 

1 

1 

4.45 

i 

25 

252 

620 

553 

163 

46 

16 

9 

4 

1 

1,690 

4.13 

.32 

Table  151  shows  the  classification  of  generation  13,  minus-selection  series.     This  is  an 
enlargement  of  table  28  of  Castle  and  Phillips. 

TABLE  151. 


Grade  of  offspring  (minus)  . 

Grade  of 
parents. 

Totals. 

Means. 

Regres- 
sion. 

H 

2 

21 

21 

23 

I 

;*i 

Si 

-21 

7 

43 

25 

28 

12 

1 

116 

2.25 

0 

-2f 

S 

74 

80 

87 

56 

19 

5 

329 

2.39 

0 

-21 

8 

65 

65 

92 

46 

11 

2 

i 

290 

2.38 

.12 

-2f 

3 

23 

33 

58 

44 

4 

4 

i 

170 

2.50 

.12 

-23 

1 

5 

4 

16 

12 

7 

1 

46 

2.56 

.19V 

-2J 

7 

8 

10 

7 

2 

34 

2.42 

.45 

-3 

4 

1 

6 

5 

3 

2 

21 

2.59 

.41 

-2.49 

27 

221 

216 

297 

182 

47 

14 

2 

1,006 

2.40 

.09 

TABLES. 


185 


Table  152  shows  the  classification  of  generation  14,  minus-selection  series. 

TABLE  152. 


Grade  of 
parents. 

Grade  of  offspring  (minus). 

Totals. 

Means. 

Regres- 
sion. 

1 

a 

U 

ii 

2 

21 

2J 

2! 

3 

3i 

31 

-2i 
-2| 
-2i 
-2| 
-2| 
-2| 
-3 
-31 
-31 
-3f 

2 

8 

40 
23 

7 
6 
1 

2 
20 
50 
32 
20 
10 
1 
6 

14 

22 
73 
59 
42 
25 
15 
3 

8 
11 
29 

44 
43 
14 
8 
7 
4 
4 

26 
65 
199 
172 
127 
58 
33 
20 
7 
10 

2.54 
2.40 
2.36 
2.44 
2.60 
2.52 
2.69 
2.56 
2.85 
2.75 

-.29 
-.03 
.14 
.18 
.15 
.35 
.31 
.56 
.40 
.62 

2 
8 

2 

2 
2 

10 
11 
2 
3 
4 
3 
3 

1 
1 

4 
2 
5 

1 

1 

3 

» 

» 

7 

SO 

-2.64 

1 

141 

256 

172 

40 

13 

1 

717 

2.48 

.16 

Table  153  shows  the  classification  of  generation  15,  minus-selection  series. 

TABLE  153. 


Grade  of 
parents. 

Grade  of  offspring  (minus)  . 

Totals. 

Means. 

Regres- 
sion. 

11 

2 

21 

2* 

2! 

3 

31 

3J 

-21 

-21 
-2| 

-2| 

-2| 
-2| 

-25 
-3 
-3| 
-31 

i 

2 

1 

1 
11 

15 
39 
41 
7 
4 

4 
23 
24 
65 
97 
37 
18 
1 
4 

4 
15 
47 
102 
137 
91 
62 
17 
11 
5 

491 

4 
13 
29 
68 
99 
70 
70 
16 
17 
12 

13 
64 
119 
290 
407 
240 
183 
51 
42 
29 

2.46 
2.39 
2.45 
2.49 
2.50 
2.60 
2.64 
2.76 
2.73 
2.85 

-.33 
-.14 
-.07 
.01 
.12 
.15 
.23 
.24 
.34 
.60 

2 
3 
14 

24 
31 
22 
13 

7 
8 

6 
3 

7 
4 
1 
3 

2 

1 

2 
1 

273 

-2.65 

4 

118 

398 

124 

24 

6 

1,438 

2.54 

.11 

Table  154  shows  the  classification  of  generation  16,  minus-selection  series. 

TABLE  154. 


Grade  of 
parents. 

Grade  of  offspring  (minus)  . 

Totals. 

Means. 

Regres- 
sion. 

1 

11 

u 

11 

2 

3 
5 
4 

10 
10 

11 

2 

21 

5 

4 
27 
56 
36 
45 
12 
6 

2i 

1 
3 

61 
188 
130 
187 
95 
30 

2} 

3 

31 

31 

*l 

4 

-21 
-2| 

-21 
-2| 
-2| 
-2| 

-3 
-3* 
-31 

9 
14 
152 
450 
362 
563 
316 
98 
16 

2.19 
2.16 
2.55 

2.58 
2.62 
2.66 
2.73 
2.74 
2.83 

.06 
.21 
-.05 
.04 
.13 
.21 
.27 
.38 
.42 

1 

1 
56 
148 
151 
230 
128 
36 
12 

3 
36 
28 
71 
65 
15 
3 

1 
5 

5 
10 
12 
10 
1 

1 
1 
1 

1 
1 
1 
1 

I 

i 

-2.79 

1 

3 

51 

191 

695 

762 

221 

50 

4 

1 

1 

1,980 

2.63 

.16 

186 


INHERITANCE    IN   RATS. 


Tal  le  155  shows  the  classification  of  generation  17,  minus-sf  lection  series. 

TABLE  155. 


Grade  of 
parents. 

Grade  of  offspring  (minus). 

Totals. 

Means. 

Regres- 
sion. 

H 

2 

21 

2i 

2J 

3 

3i 

3i 

3| 

4. 

4* 

-2f 
-2! 
-2J 
-3 
-3t 
-3i 
-3f 

i 

2 

2 

4 

10 
12 
34 
3 

40 
77 
110 
28 
5 
3 

49 

81 
145 
42 
18 
16 

11 

28 
51 
18 
17 
15 
1 

1 
1 

19 
7 
6 

6 

113 
202 
364 
98 
48 
41 
2 

-2.63 
-2.65 
-2.71 
-2.75 
-2.92 
-2.92 
-3.25 

0 
.10 
.16 
.25 
.20 
.33 
.12 

1 

1 

1 
1 

1 

-2.86 

i 

s 

59 

263 

351 

141 

40 

4 

1 

868 

-2.70 

.16 

Table  156  summarizes  the  results  of  the  j  lus-selection  of  hooded  rats  continued  through 
sixteen  successive  generations. 

TABLE  156. 


Genera- 
tion. 

Mean 
grade  of 
parents. 

Mean 
grade  of 
offspring. 

Lowest 
grade  of 
offspring. 

Highest 
grade  of 
offspring. 

Standard 
deviation 
of 
offspring. 

Correla- 
tion, 
parents- 
offspring. 

Number  of 
offspring. 

1 

2.51 

2.05 

+  1.00 

+3.00 

.54 

.29 

150 

2 

2.52 

1.92 

-1.00 

+3.75 

.73 

.31 

471 

3 

2.73 

2.51 

+   .75 

+4.00 

.53 

.33 

341 

4 

3.09 

2.73 

+   .75 

+3.75 

.47 

.06 

444 

5 

3.33 

2.90 

+   .75 

+4.25 

.50 

.16 

610 

6 

3.52 

3.11 

+1.50 

+4.50 

.49 

.18 

861 

7 

3.56 

3.20 

+1.50 

+4.75 

.55 

.21 

1,077 

8 

3.75 

3.48 

+1.75 

+4.50 

.44 

.09 

1,408 

9 

3.78 

3.54 

+1.75 

+4.50 

.35 

.21 

1,322 

10 

3.88 

3.73 

+2.25 

+5.00 

.36 

.11 

776 

11 

3.98 

3.78 

+2.75 

+5.00 

.29 

.23 

697 

12 

4.10 

3.92 

+2.25 

+5.25 

.31 

.16 

682 

13 

4.13 

3.94 

+2.75 

+5.25 

.34 

.13 

529 

14 

4.14 

4.01 

+2.75 

+5.50 

.34 

.31 

1,359 

15 

4.38 

4.07 

+2.50 

+5.50 

.29 

.30 

3,690 

16 

4.45 

4.13 

+3.25 

+5.87 

.29 

.31 

1,690 

Total 

16,107 

TABLES. 


187 


Table  ]57  summarizes  the  results  of  the  minus-selection  of  hooded  rats  continued 
through  seventeen  successive  generations. 

TABLE  157. 


Genera- 
tion. 

Mean 
grade  of 
parents. 

Mean 
grade  of 
offspring. 

Lowest 
grade  of 
offspring. 

Highest 
grade  of 
offspring. 

Standard 
deviation 
of 
offspiing. 

Correla- 
tion, 
parents- 
offspring. 

Number  of 
offspring. 

1 

-1.46 

-1.00 

+   .25 

-2.00 

.51 

55 

2 

-1.41 

-1.07 

+   .50 

-2.00 

.49 

-io3 

132 

3 

-1.56 

-1.18 

0 

-2.00 

.48 

.20 

195 

4 

-1.69 

-1.28 

+   .50 

-2.25 

.46 

.02 

329 

5 

-1.73 

-1.41 

0 

-2.50 

.50 

.18 

701 

6 

-1.86 

-1.56 

0 

-2.50 

.44 

.16 

1,252 

7 

-2.01 

-1.73 

0 

-2.75 

.35 

.14 

1,680 

8 

-2.05 

-1.80 

0 

-2.75 

.28 

.09 

1,726 

9 

-2.11 

-1.92 

-    .50 

-2.75 

.28 

.05 

1,591 

10 

-2.18 

-2.01 

-1.00 

-3.25 

.24 

.15 

1,451 

11 

-2.30 

-2.15 

-1.00 

-3.50 

.35 

.08 

984 

12 

-2.44 

-2.23 

-1.00 

-3.50 

.37 

.40 

1,037 

13 

-2.48 

-2.39 

-1.75 

-3.50 

.34 

.18 

1,006 

14 

-2.64 

-2.48 

-1.00 

-3.50 

.30 

.28 

717 

15 

-2.65 

-2.54 

-1.75 

-3.50 

.29 

.35 

1,438 

16 

-2.79 

-2.63 

-1.00 

-4.00 

.27 

.26 

1,980 

17 

-2.86 

-2.70 

-1.75 

-4.25 

.28 

.22 

868 

Total 

17,142 

Table  158  shows  the  classification  of  the  F2  young  obtained  by  crossing  homozygous 
'mutant"  with  wild  rats. 

TABLE  158. 


Mutant  grandparents. 

Grade  of  off- 
spring. 

Totals. 

5 

5i 

5J 

5! 

5* 

6 

90630,  +5J  

3 
2 

12 
22 
12 
3 

9 
29 
11 
1 

2 
1 

20 
59 
19 
5 

46 
114 
42 
10 

90698,  +5J  

1 

90694,  +5i  

90630,  +5},  or  0636,  +5i  

1 

Total  

1 

6 

49 

50 

3 

103 

212 

BIBLIOGRAPHY. 

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190  INHERITANCE   IN   RATS. 

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EXPLANATION  OF  PLATES. 

PLATE  1. 

Colored  photographs  of  the  fur  of  guinea-pigs,  showing  grades  of  dilution  due  to  different 
combinations  of  the  allelomorphs  of  albinism.  The  skin  of  each  animal  from  which 
fur  is  shown  was  opened  along  the  median  ventral  line  and  a  complete  section  across 
the  middle  of  the  body  is  shown  in  skins  1,  6,  9, 10,  and  11.  But  in  the  other  skins  2, 3, 
4,  5,  7,  and  8,  only  a  section  extending  from  the  mid-dorsal  to  the  mid-ventral  line  is 
shown.  Figures  1  to  4  show  agouti  fur  (AAEE) ;  5  to  8,  non-agouti  fur  (aaEE) ;  and 
9  to  11  show  fur  in  which  the  extension  factor  is  wanting  (ee).  The  uppermost  row  of 
skins  are  intense  pigmented,  all  others  are  dilute  of  intensities,  diminishing  toward 
the  bottom  of  the  plate.  Factors  A  and  E  are  written  as  homozygous,  though  this  is 
not  known  in  all  cases. 

FIG.    1.  Black-red  agouti C    C    AAEE 

2.  Dark  sepia-yellow  agouti Cd  Cd  AAEE 

3.  Dark  sepia-cream  agouti Cd  CT  AAEE 

4.  Light  sepia-cream  agouti Cd  Ca  AAEE 

5.  Black C    C    aaEE 

6.  Dark  sepiai Cd  Cd  aaEE 

7.  Dark  sepia2 Cd  Cr  aaEE 

8.  Light  sepias Cd  Ca  aaEE 

9.  Red C    C    aaee 

10.  "Yellow4 Cd  Cd  aaee 

11.  Creame Cd  Ca  aaee  (Cd  Cr  similar) 

PLATE  2. 

Photographs  of  guinea-pig  skins,  showing  further  grades  of  reduction  in  color  due  to  albin- 
ism and  its  allelomorphs.  Sections  of  skin  extending  entirely  across  the  body  are  shown 
in  all  cases.  The  arrangement  is  similar  to  that  of  plate  1. 

FIQ.  12.  Dark  sepia-white  agouti  (red-eyed) Q-  Cr  AAEE 

13.  Light  sepia-white  agouti  (red-eyed) Cr  Ca  AAEE 

14.  Albino  (known  to  transmit  agouti) Ca  Ca  AAEE 

15.  Dark  sepia  (red-eyed) Or  Cr  aaEE 

16.  Light  sepia  (red-eyed) Cr  Ca  aaEE 

17.  Albino  (transmits  only  non-agouti) Ca  Ca  aaEE 

18.  White  (red-eyed) Cr  Cr  aaee  (Cr  Ca  similar) 

19.  Albino  (from  yellow  stock) Ca  Ca  aaee 

PLATE  3. 

Colored  photographs  of  the  skins  of  guinea-pigs. 

FIG.  20.  A  half -grown  guinea-pig  of  race  C;  color,  pale  cream.     The  eyes  were 
brown-pigmented. 

21.  An  FI  male  hybrid  whose  mother  was  an  albino  of  race  B  and  whose  father 

was  a  pure  cutleri.    Compare  figures  23  and  34. 

22.  An  Fi  male  hybrid  whose  mother  was  a  brown-eyed  cream  animal  of  race  C 

and  whose  father  was  a  pure  cutleri.    Compare  figures  20  and  23. 

23.  A  pure  cutleri  male. 

24.  A  pure  cutleri  female. 

PLATE  4. 

Colored  photographs  of  the  skins  of  F2  hybrids  produced  by  crossing  brown-eyed  cream 
guinea-pigs  with  Cavia  cutleri.     Compare  figures  20,  22,  and  23. 
FIG.  25.  Golden  agouti. 

26.  Pale  black  (sepia). 

27.  Brown  or  chocolate. 

28.  Cinnamon. 

29.  Yellow. 

30.  Albino. 

191 


192  EXPLANATION   OF   PLATES. 

PLATE  5. 

Colored  photographs  of  skins  showing  new  color  varieties  of  guinea-pigs. 
FIG.  31.  Silver  cinnamon  or  red-eyed  cinnamon. 

32.  Red-and-pink-eyed  black  spotted  with  white. 

33.  Pink-eyed  golden  agouti  spotted  with  red  and  with  white,  hence  a  "tri- 

color." 

34.  Albino  with  sooty  fur  and  black  pigmented  extremities,  similar  to  race  B. 

PLATE  6. 

Femurs  of  hybrid  guinea-pigs  and  of  their  parent  races,  natural  size,  to  show  extent  of 
variation.  The  longest  and  the  shortest  femur  in  each  group  of  individuals  is  shown 
with  3  or  4  others  of  intermediate  length  placed  between  them.  In  the  left  half  of  the 
plate  are  shown  the  femurs  of  males,  and  in  the  right  half  the  femurs  of  females. 
Top  row,  Cavia  cutleri.  Second  row,  race  B  guinea-pigs.  Third  row,  Fi  hybrids  pro- 
duced by  the  cross  of  C.  cutleri  cf  X  race  B  9 .  Fourth  row,  F2  hybrids  from  the  same 
cross. 

PLATE  7. 

FIG.  35.  A  scale  of  grades  used  in  describing  the  pattern  of  piebald  rats.  Rats  like  the 
pictures  toward  the  left  of  the  scale  are  known  to  fanciers  as  "hooded" ;  the  grade 
at  the  extreme  right  would  be  called  "Irish"  by  fanciers. 

36.  Skins  of  a  pair  of  rats  and  of  their  9  young.     One  parent  was  an  "Irish"  rat,  the 

other  "hooded."  Four  of  the  young  are  hooded,  five  are  Irish.  Hooded  is  re- 
cessive to  Irish  in  crosses.  The  Irish  parent  in  this  case  was  a  heterozygote. 
Note  individual  variation  in  each  group  of  young. 

37.  A  typical  smooth-coated  guinea-pig. 

38.  A  rough-coated  guinea-pig,  well-rosetted,  grade  A. 

39.  A  poorly-rosetted  rough  guinea-pig,  grade  C. 


PLATE    1 


Variations  of  intensity  of  coat  pigments,  due  to  albino  allelomorphs,  in  agouti  series  (1 — 4), 
black  series  (5 — 8),  and  yellow  series  (9 — 11). 


PLATE    2 


Albinism  and    its    non-yellow    allelomorphs    in    agouti   series    (12 — 14),   black   series 
(15 — 17),  and  yellow  series  (18,  19). 


20 


21 


22 


24 


Fig.  20,  half-grown  guinea-pig,  race  C.  Figs.  23,  24,  male  and  female  Cavia  cutleri,  adult. 
Fig.  22,  F!  hybrid,  race  C  x  Cavia  cutleri,  adult.  Fig.  21,  Fx  hybrid,  race  B  (Plate  5, 
Fig.  34)  x  Cavia  cutleri,  adult. 


25 


26 


27 


28 


29 


30 


F2  hybrids,  race  C  x  Cavia  cutleri.     Fig.  25,  agouti;  26,  black;  27,  chocolate;  28,  cinnamon; 
29,  yellow;  30,  albino. 


31 


32 


33 


34 


Some  new  guinea-pig  color  varieties.  Fig.  31,  red-eyed  cinnamon;  32,  red-and-pink-eyed 
black  spotted  with  white;  33,  pink-eyed  golden  agouti  spotted  with  red  and  with  white; 
34,  albino  with  sooty  fur  and  black  pigmented  extremities,  similar  to  race  B. 


PLATE    6 


Femurs  of  Cavia  cutleri  (male  and  female),  of  race  B,  and  of  their  F;  and  F2  hybrids,  showing 
complete  range  of  variation  in  each.     Natural  size. 


36 


35 


37 


38 


39 


Fig.  35,  a  scale  of  grades  for  piebald  rats.  Fig.  36,  a  pair  of  piebald  rats  and  their  nine 
young.  Fig.  37,  a  smooth  guinea-pig.  Fig.  38,  a  well-rosetted  rough  guinea-pig,  grade 
A.  big.  39,  a  poorly  rosetted  rough  guinea-pig,  grade  C. 


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